Preconditions

Preconditions are tags you add to your changelog or individual changesets to control the execution of an update based on the state of the database. Preconditions let you specify security and standardization requirements for your changesets. If a precondition on a changeset fails, Liquibase does not deploy that changeset.

Uses

You can use preconditions to:

Document what assumptions the author of the changelog had when creating it.
Enforce that those assumptions are not violated by users running the changelog.
Perform data checks before performing an unrecoverable change such as dropTable.
Control what changesets are run and not run based on the state of the database.

You can use all Liquibase preconditions in XML, YAML, and JSON changelogs. The only supported precondition for SQL changelogs is sqlCheck. For a list of preconditions, see Available preconditions.

Syntax

You can use one local <preConditions> tag per changeset and one global <preConditions> tag in the changelog (outside any changeset). In XML, YAML, and JSON changelogs, you can use conditional logic to add multiple preconditions within a single <preConditions> tag.

Preconditions at the changelog level are applied to all changesets, not just those listed in the current changelog or its child changelogs.

The following example XML, YAML, and JSON changelogs will only be run if the database executed against is Oracle and the database user executing the script is SYSTEM. Also, they will run the changeset with the sqlCheck precondition and createTable. The example SQL changelog only runs the sqlCheck precondition and createTable.

If the preconditions check fails, you will receive a warning and it will continue executing the changeset as normal because of the onFail="WARN" precondition. To prevent the execution of the changeset when the precondition fails, you can set HALT or CONTINUE values. For more information, see onFail/onError values.

XML example

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext"
    xmlns:pro="http://www.liquibase.org/xml/ns/pro"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
        http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd
        http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd
        http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-latest.xsd">

    <preConditions>
        <dbms  type="oracle"  />
        <runningAs  username="SYSTEM"  />
    </preConditions>

    <changeSet  id="1"  author="Liquibase User">
        <preConditions  onFail="WARN">
            <sqlCheck  expectedResult="0">SELECT COUNT(*) FROM example_table</sqlCheck>
        </preConditions>
        <comment>Comments should go after the precondition. Otherwise, Liquibase returns an error.</comment>

        <createTable  tableName="example_table">
            <column name="id" type="int" autoIncrement="true">
                <constraints primaryKey="true" nullable="false">
            </column>
            <column name="firstname" type="varchar(50)">
            <column name="lastname" type="varchar(50)">
                <constraints nullable="false">
            </column>
            <column name="state" type="char(2)">
        </createTable>
    </changeSet>
</databaseChangeLog>

SQL example

-- liquibase formatted sql
			
-- changeset Liquibase User:1
-- preconditions onFail:WARN 
-- precondition-sql-check expectedResult:0 SELECT COUNT(*) FROM example_table
-- comment: /* Comments should go after the precondition. Otherwise, Liquibase returns an error. */
create table example_table (  
	id int primary key,
	firstname varchar(50),
	lastname varchar(50) not null,
	state char(2)
)

YAML example

databaseChangeLog:
 - preConditions:
     - dbms:
        type: oracle
     - runningAs:
        username: SYSTEM
 - changeSet:
     id:  1
     author: Liquibase User
     preConditions:
       - onFail: WARN
       - sqlCheck:
          expectedResult: 0
          sql: SELECT COUNT(*) FROM example_table
     comment: Comments should go after the precondition. Otherwise, Liquibase returns an error.
     changes:
     - createTable:
         tableName: example_table
         columns:
          - column:
             name: id
             type: int
             autoIncrement: true
             constraints:
              primaryKey: true
              nullable: false
          - column:
             name:  firstname
	         type:  varchar(50)
          - column:
             name:  lastname
             type:  varchar(50)
             constraints:
              nullable:  false
          - column:
             name:  state
             type:  char(2)

JSON example

{
  "databaseChangeLog": [
    {
      "preConditions": [
        {
          "dmbs": {
            "type": "oracle"
          }
        },
        {
          "runningAs": {
            "username": "SYSTEM"
          }
        }
      ],
      "changeSet": {
        "id": "1",
        "author": "Liquibase User",
        "preConditions": [
          {
            "onFail": "WARN"
          },
          {
            "sqlCheck": {
              "expectedResult": 0,
              "sql": "SELECT COUNT(*) FROM example_table"
            }
          }
        ],
        "comment": "Comments should go after the precondition. Otherwise, Liquibase returns an error.",
        "changes": [
          {
            "createTable": {
              "tableName": "example_table",
              "columns": [
                {
                  "column": {
                    "name": "id",
                    "type": "int",
                    "autoIncrement": true,
                    "constraints": {
                      "primaryKey": true,
                      "nullable": false
                    }
                  }
                },
                {
                  "column": {
                    "name": "firstname",
                    "type": "varchar(50)"
                  }
                },
                {
                  "column": {
                    "name": "lastname",
                    "type": "varchar(50)",
                    "constraints": {
                      "nullable": false
                    }
                  }
                },
                {
                  "column": {
                    "name": "state",
                    "type": "char(2)"
                  }
                }
              ]
            }
          }
        ]
      }
    }
  ]
}

Multiple preconditions

In XML, JSON, and YAML changelogs, you can set multiple preconditions in one <preConditions> tag by using nestable AND, OR, and NOT conditional logic tags. If no conditional tags are specified, the default value is AND.

Liquibase uses lazy evaluation (call-by-need) when running preconditions. For example, if the first condition of an AND expression fails, Liquibase does not evaluate the second condition. If the first condition of an OR expression succeeds, Liquibase does not evaluate the second condition.

XML:

<preConditions>
    <or>
        <CONDITION_1>
        <CONDITION_2>
    </or>
</preConditions>

YAML:

- preConditions:
    - or:
        - CONDITION_1
        - CONDITION_2

JSON:

{
  "preConditions": [
    {
      "or": [
        {
          {CONDITION_1}
        },
        {
          {CONDITION_2}
        }
      ]
    }
  ]
}

Examples

The following syntax example will check that the update is running on Oracle and with the SYSTEM user but will only generate a warning message if the precondition fails:

<preConditions  onFail="WARN">
    <dbms  type="oracle"  />
    <runningAs  username="SYSTEM"  />
</preConditions>

The following will require running the changelog on Oracle or MySQL:

<preConditions>
   <or>
      <dbms  type="oracle"  />
      <dbms  type="mysql"  />
   </or>
</preConditions>

You can also see the precondition running as SYSTEM if executing against an Oracle database or running as SA if executing against a MS SQL database.

<preConditions>
    <or>
       <and>
          <dbms  type="oracle"  />  
          <runningAs  username="SYSTEM"  />
       </and>
       <and>
          <dbms  type="mssql"  />
          <runningAs  username="sa"  />
       </and>
     </or>
</preConditions>

Handling failures and errors

Liquibase defines two types of preconditions:

Precondition failures which represent that the check failed
Precondition errors that are the exceptions thrown in the execution of a check

The process of both can be controlled through the onFail and onError attributes on the <preConditions> tag.

Available attributes

Attribute	Description
`onError`	Controls what happens if there is an error checking whether the precondition passed or not.
`onErrorMessage`	Provides a custom message to output when preconditions fail. Since 2.0
`onFail`	Controls what happens if the preconditions check fails.
`onFailMessage`	Provides a custom message to output when preconditions fail. Since 2.0
`onSqlOutput`	Controls how preconditions are evaluated in the `update-sql` mode for XML, YAML, and JSON changelogs. Since 1.9.5
`onUpdateSql`	Controls how preconditions are evaluated in the `update-sql` mode for formatted SQL changelogs.

`onFail`/`onError` values

Value	Description
`CONTINUE`	Skips over the changeset. Execution of the changeset will be attempted again on the next update. Continues with the changelog.
`HALT`	Halts the execution of the entire changelog (default). `HALT` can be put outside a changeset (e.g. at the beginning of the changelog).
`MARK_RAN`	Skips over the changeset but mark it as executed. Continues with the changelog.
`WARN`	Sends a warning and continues executing the changeset / changelog as normal. `WARN` can be put outside a changeset (e.g. at the beginning of the changelog).

`onSqlOutput`/`onUpdateSql` values

Value	Description
`FAIL`	Fails the `preCondition` in the `update-sql` mode.
`IGNORE`	Ignores the `preCondition` in the `update-sql` mode (default).
`TEST`	Runs the changeset in the `update-sql` mode.

Failures and errors will cause Liquibase to return non-zero exit codes in command output. Warnings will cause Liquibase to return exit codes of zero.

Example failures/errors

The following is a sample failure on a changelog:

Unexpected error running Liquibase: Validation Failed:
1 preconditions failed
myChangelog.xml : DBMS Precondition failed: expected oracle, got postgresql

The following is a sample error on a changelog:

Unexpected error running Liquibase: Validation Failed:
1 preconditions generated an error
myChangelog.xml : liquibase.precondition.core.SqlPrecondition@5745ca0e : ERROR: relation "public.table_does_not_exist" does not exist

The following is a sample warning on a changeset:

WARNING: Executing myChangelog.xml::01-new::wonder.woman despite precondition failure due to onFail='WARN':
1 preconditions failed
myChangelog.xml : Column public.customer.name_new does not exist

Available preconditions

The examples of preconditions shown in the table doesn't include the schemaName attribute. It is best practice not to keep the schemaName in the changeset and rely on the default schema except for times you don’t want to create something in the default schema.

Additionally, you can include the onError or onFail attributes with the WARN, HALT, CONTINUE, or MARK_RAN value in the preconditions tag, however, the CONTINUE and MARK_RAN options can only be applied to preconditions inside a changeset.

`changeLogPropertyDefined`

Checks whether given changelogattribute is present. It fails if the value is not the same as given.

Attribute	Description	Requirement
`property`	The name of the property to check.	Required
`value`	The required value for a given property.	Optional

XML example

<preConditions onFail="WARN">
    <changeLogPropertyDefined property="myproperty"
                              value="requiredvalue"/>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - changeLogPropertyDefined:
       property: myproperty
       value: requiredvalue

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "changeLogPropertyDefined": {
        "property": "myproperty",
        "value": "requiredvalue"
      }
    }
  ]
}

`changeSetExecuted`

Defines if the specified changeset has already been executed.

Attribute	Description	Requirement
`id`	The changeset id.	Required
`author`	The changeset author.	Required
`changeLogFile`	The file name (including searchPath relative path) of the changeset.	Required

XML example

<preConditions onFail="HALT">
    <changeSetExecuted id="1"
                       author="liquibase"
                       changeLogFile="changelog.xml" />
</preConditions>

YAML example

- preConditions:
    - onFail: HALT
    - changeSetExecuted:
       id: 1
       author: liquibase
       changeLogFile: changelog.xml

JSON example

{
  "preConditions": [
    {
      "onFail": "HALT"
    },
    {
      "changeSetExecuted": {
        "id": "1",
        "author": "liquibase",
        "changeLogFile": "changelog.xml"
      }
    }
  ]
}

`columnExists`

Defines if the specified column exists in the database.

Attribute	Description	Requirement
`columnName`	The name of the column.	Required
`tableName`	The name of the column's table.	Required
`schemaName`	The name of the table's schema.	Optional

XML example

<preConditions onFail="WARN">
    <columnExists tableName="table1"
                  columnName="column1" />
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - columnExists:
       tableName: table1
       columnName: column1

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "columnExists": {
        "tableName": "table1",
        "columnName": "column1"
      }
    }
  ]
}

`dbms`

Defines if the database executed against matches the type specified.

Attribute	Description	Requirement
`type`	The type of database expected. Multiple dbms values can be specified using comma-separated values.	Required

XML example

<preConditions onFail="WARN">
  <or>
    <dbms  type="oracle"  />
    <dbms  type="mysql"  />
  </or>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - or:
       - dbms:
          type: oracle
       - dbms:
          type: mysql

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "or": [
        {
          "dbms": {
            "type": "oracle"
          }
        },
        {
          "dbms": {
            "type": "mysql"
          }
        }
      ]
    }
  ]
}

`foreignKeyConstraintExists`

Defines if the specified foreign key exists in a table in the database.

Attribute	Description	Requirement
`foreignKeyName`	The name of the foreign key.	Required
`foreignKeyTableName`	The name of the table the foreign key is in.	Required in 4.7.0+
`schemaName`	The name of the foreign key's schema.	Optional

XML example

<preConditions onFail="WARN">
    <foreignKeyConstraintExists foreignKeyName="PK_2354"
                                foreignKeyTableName="myTable" />
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - foreignKeyConstraintExists:
       foreignKeyName: PK_2354
       foreignKeyTableName: myTable

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "foreignKeyConstraintExists": {
        "foreignKeyName": "PK_2354",
        "foreignKeyTableName": "myTable"
      }
    }
  ]
}

`indexExists`

Defines if the specified index exists in the database. You can either specify the indexName attribute or tableName and columnNames attributes.

Note: There are a few databases where the indexName is not unique, which is why both indexName and tableName can be used.

Attribute	Description	Requirement
`indexName`	The name of the index.	Optional
`columnNames`	The name of the column.	Optional
`tableName`	The name of the table.	Optional
`schemaName`	The name of the index's schema.	Optional

XML example

<preConditions onFail="WARN">
    <indexExists indexName="originindex"/>
</preConditions>

<preConditions onFail="WARN">
    <indexExists tableName="MY_NEW_TABLE"
                 columnNames="ID"/>
</preConditions>

<preConditions onFail="WARN">
    <indexExists indexName="originindex"
                 tableName="MY_NEW_TABLE"/>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - indexExists:
       indexName: originindex

- preConditions:
    - onFail: WARN
    - indexExists:
       tableName: MY_NEW_TABLE
       columnNames: ID

- preConditions:
    - onFail: WARN
    - indexExists:
       indexName: originindex
       tableName: MY_NEW_TABLE

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "indexExists": {
        "indexName": "originindex"
      }
    }
  ]
}

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "indexExists": {
        "tableName": "MY_NEW_TABLE",
        "columnNames": "ID"
      }
    }
  ]
}

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "indexExists": {
        "indexName": "originindex",
        "tableName": "MY_NEW_TABLE"
      }
    }
  ]
}

`primaryKeyExists`

Defines if the specified primary key exists in the database.

Attribute	Description	Requirement
`primaryKeyName`	The name of the primary key constraint.	`tableName` or `primaryKeyName` is required
`tableName`	the name of the table containing primary key.	`tableName` or `primaryKeyName` is required
`schemaName`	The name of the primary key's schema.	Optional

XML example

<preConditions onFail="HALT">
    <primaryKeyExists primaryKeyName="ID_2354"
                      tableName="table1" />
</preConditions>

YAML example

- preConditions:
    - onFail: HALT
    - primaryKeyExists:
       primaryKeyName: ID_2354
       tableName: table1

JSON example

{
  "preConditions": [
    {
      "onFail": "HALT"
    },
    {
      "primaryKeyExists": {
        "primaryKeyName": "ID_2354",
        "tableName": "table1"
      }
    }
  ]
}

`rowCount`

Checks that the number of rows in a table matches an expected value.

Attribute	Description	Requirement
`expectedRows`	The number of rows the user expects in a table.	Required
`tableName`	The name of the column's table.	Required

XML example

<preConditions onFail="WARN">
    <rowCount expectedRows="5"
              tableName="person"/>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - rowCount:
       expectedRows: 5
       tableName: person

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "rowCount": {
        "expectedRows": "5",
        "tableName": "person"
      }
    }
  ]
}

`runningAs`

Defines if the database user executed under matches the username specified.

Attribute	Description	Requirement
`username`	The database user script which is expected to run as.	Required

XML example

<preConditions  onFail="WARN">
    <dbms  type="oracle"  />
    <runningAs  username="SYSTEM"  />
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - dbms:
       type: oracle
    - runningAs:
       username: SYSTEM

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "dbms": {
        "type": "oracle"
      }
    },
    {
      "runningAs": {
        "username": "SYSTEM"
      }
    }
  ]
}

`sequenceExists`

Defines if the specified sequence exists in the database.

Attribute	Description	Requirement
`sequenceName`	The name of the sequence.	Required
`schemaName`	The name of the sequence's schema.	Optional

XML example

<preConditions onFail="WARN">
    <sequenceExists sequenceName="idnumber" />
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - sequenceExists:
       sequenceName: idnumber

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "sequenceExists": {
        "sequenceName": "idnumber"
      }
    }
  ]
}

`sqlCheck`

Executes an SQL string and checks the returned value. The SQL must return a single row with a single value.

To check a number of rows, use the count SQL function.
To check for ranges of values, perform the check in the SQL and return a value that can be easily compared against.

Attribute	Description	Requirement
`expectedResult`	The value to compare the SQL result to.	Required
`sql`	In JSON and YAML changelogs, the SQL statement to run. In XML changelogs, insert the SQL statement directly within the `<sqlCheck></sqlCheck>` tags. IN SQL changelogs, insert the SQL statement directly in the precondition header.	Required

SQL example

-- changeset Liquibase User:1
-- preconditions onFail:WARN
-- precondition-sql-check expectedResult:1 SELECT COUNT(1) FROM pg_tables WHERE TABLENAME = 'myRequiredTable'
create table example_table (
	id int primary key,
	firstname varchar(50),
	lastname varchar(50) not null,
	state char(2)
)

XML example

<preConditions onFail="WARN">
    <sqlCheck expectedResult="1">
        SELECT COUNT(1)
        FROM pg_tables
        WHERE TABLENAME = 'myRequiredTable'
    </sqlCheck>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - sqlCheck:
       expectedResult: 1
       sql: SELECT COUNT(1) FROM pg_tables WHERE TABLENAME = 'myRequiredTable'

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "sqlCheck": {
        "expectedResult": "1",
        "sql": "SELECT COUNT(1) FROM pg_tables WHERE TABLENAME = 'myRequiredTable'"
      }
    }
  ]
}

`tableExists`

Defines if the specified table exists in the database.

Attribute	Description	Requirement
`tableName`	The name of the table.	Required
`schemaName`	The name of the table's schema.	Optional

XML example

<changeSet author="author" id="1">
   <preConditions onFail="MARK_RAN">
       <not>
           <tableExists tableName="MY_NEW_TABLE"/>
       </not> 
   </preConditions>

   <createTable tableName="MY_NEW_TABLE">
       <column name="IDX"
               type="${integer.type}">
           <constraints nullable="false"/> 
       </column>
       <column name="INTVAL"
               type="${integer.type}"/>
   </createTable>
</changeSet>

YAML example

- changeSet:
    preConditions:
      - onFail: MARK_RAN
      - not:
          - tableExists:
             tableName: MY_NEW_TABLE
    changes:
      - createTable:
          tableName: MY_NEW_TABLE
          columns:
            - column:
               name: INTVAL
               type: ${integer.type}
               constraints:
                 nullable: false

JSON example

{
  "changeSet": {
    "preConditions": [
      {
        "onFail": "MARK_RAN"
      },
      {
        "not": [
          {
            "tableExists": {
              "tableName": "MY_NEW_TABLE"
            }
          }
        ]
      }
    ],
    "changes": [
      {
        "createTable": {
          "tableName": "MY_NEW_TABLE",
          "columns": [
            {
              "column": {
                "name": "INTVAL",
                "type": "${integer.type}",
                "constraints": {
                  "nullable": "false"
                }
              }
            }
          ]
        }
      }
    ]
  }
}

`uniqueConstraintExists`

Checks for the existence of unique constraints before running the update. (since Liquibase 4.9.0)

Attribute	Description	Requirement
`tableName`	The name of the column's table.	Required
`columnNames`	The name of the column.	Optional
`constraintName`	The name of the unique constraint.	Optional

XML example

<preConditions onFail="WARN">
    <uniqueConstraintExists constraintName="uq_constraint_name"
                            tableName="test_table"/>
</preConditions>

<preConditions onFail="WARN">
    <uniqueConstraintExists tableName="test_table"
                            columnNames="first_name, last_name"/>
</preConditions>

YAML example

- preConditions:
    - onFail: WARN
    - uniqueConstraintExists:
       constraintName: uq_constraint_name
       tableName: test_table

- preConditions:
    - onFail: WARN
    - uniqueConstraintExists:
       tableName: test_table
       columnNames: first_name, last_name

JSON example

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "uniqueConstraintExists": {
        "constraintName": "uq_constraint_name",
        "tableName": "test_table"
      }
    }
  ]
}

{
  "preConditions": [
    {
      "onFail": "WARN"
    },
    {
      "uniqueConstraintExists": {
        "tableName": "test_table",
        "columnNames": "first_name, last_name"
      }
    }
  ]
}

`viewExists`

Defines if the specified view exists in the database.

Attribute	Description	Requirement
`viewName`	The name of the view.	Required
`schemaName`	The name of the view's schema.	Optional

XML example

<preConditions onFail="HALT">
    <viewExists viewName="liquibase" />
</preConditions>

YAML example

- preConditions:
    - onFail: HALT
    - viewExists:
       viewName: liquibase

JSON example

{
  "preConditions": [
    {
      "onFail": "HALT"
    },
    {
      "viewExists": {
        "viewName": "liquibase"
      }
    }
  ]
}

`customPrecondition`

Can be created by adding a class that implements the liquibase.precondition.CustomPrecondition interface. Parameters on custom classes are set through reflection based on the <param> sub-tags. Pass parameters as strings to the custom precondition.

Attribute	Description	Requirement
`className`	The name of the custom precondition class.	Required

`<param>` sub-tag

The parameter to pass to the custom precondition.

Attribute	Description	Requirement
`name`	The name of the parameter to set.	Required
`value`	A string value to set parameter to.	Required

XML example

<customPrecondition className="com.example.CustomTableCheck">
     <param name="tableName"
            value="our_table"/>
     <param name="count"
            value="42"/>
</customPrecondition>

YAML example

- customPrecondition:
    - className: com.example.CustomTableCheck
    - param:
       name: tableName
       value: our_table
    - param:
       name: count
       value: 42

JSON example

{
  "customPrecondition": [
    {
      "className": "com.example.CustomTableCheck"
    },
    {
      "param": {
        "name": "tableName",
        "value": "our_table"
      }
    },
    {
      "param": {
        "name": "count",
        "value": "42"
      }
    }
  ]
}

Preconditions

Uses

Syntax

Multiple preconditions

Examples

Handling failures and errors

Available attributes

onFail/onError values

onSqlOutput/onUpdateSql values

Example failures/errors

Available preconditions

changeLogPropertyDefined

changeSetExecuted

columnExists

dbms

foreignKeyConstraintExists

indexExists

primaryKeyExists

rowCount

runningAs

sequenceExists

sqlCheck

tableExists

uniqueConstraintExists

viewExists

customPrecondition

<param> sub-tag

`onFail`/`onError` values

`onSqlOutput`/`onUpdateSql` values

`changeLogPropertyDefined`

`changeSetExecuted`

`columnExists`

`dbms`

`foreignKeyConstraintExists`

`indexExists`

`primaryKeyExists`

`rowCount`

`runningAs`

`sequenceExists`

`sqlCheck`

`tableExists`

`uniqueConstraintExists`

`viewExists`

`customPrecondition`

`<param>` sub-tag