MERGE

Capella Operational

reference

A MERGE statement provides the ability to update, insert into, or delete from a keyspace based on the results of a join with another keyspace or subquery. It is possible to specify actions (insert, update, delete) on the keyspace based on a match or no match in the join. Multiple actions can be specified in the same query.

Couchbase Capella supports two types of merge clause, which are described in the sections below: ANSI Merge and Lookup Merge.

The ANSI merge clause has much more flexible functionality than its earlier legacy equivalent. Since it is standard compliant and more flexible, we recommend you to use ANSI merge exclusively, where possible.

Privileges

User executing the MERGE statement must have the following privileges:

Query Select privileges on the source keyspace
Query Insert, Query Update, or Query Delete privileges on the target keyspace as per the MERGE actions
Query Select privileges on the keyspaces referred in the RETURNING clause

For more details about user roles, refer to Authorization.

A user with the Data Writer privilege may set documents to expire. When the document expires, the data service deletes the document, even though the user may not have the Query Delete privilege.

Syntax

merge ::= 'MERGE' 'INTO' ( ansi-merge | lookup-merge ) limit-clause? returning-clause?

ansi-merge	ANSI Merge
lookup-merge	Lookup Merge
limit-clause	LIMIT Clause
returning-clause	RETURNING Clause

ANSI Merge

ansi-merge ::= target-keyspace use-index-clause 'USING' ansi-merge-source
               ansi-merge-predicate ansi-merge-actions

target-keyspace	ANSI Merge Target
use-index-clause	ANSI Merge Target Hint
ansi-merge-source	ANSI Merge Source
ansi-merge-predicate	ANSI Merge Predicate
ansi-merge-actions	ANSI Merge Actions

ANSI Merge Target

target-keyspace ::= keyspace-ref ( 'AS'? alias )?

The merge target is the keyspace which you want to update, insert into, or delete from.

keyspace-ref	Keyspace Reference
alias	AS Alias

Keyspace Reference

keyspace-ref ::= keyspace-path | keyspace-partial

keyspace-path ::= ( namespace ':' )? bucket ( '.' scope '.' collection )?

keyspace-partial ::= collection

Keyspace reference for the merge target. For more details, refer to Keyspace Reference.

AS Alias

Assigns another name to the keyspace reference. For details, refer to AS Clause.

Assigning an alias to the keyspace reference is optional. If you assign an alias to the keyspace reference, the AS keyword may be omitted.

ANSI Merge Target Hint

You can use a USE INDEX hint on the merge target to specify that the merge should use a particular index. For details, refer to USE INDEX Clause.

The USE INDEX hint is the only hint allowed on the target. You cannot specify a USE KEYS hint or a join hint (USE NL or USE HASH) on the target of a merge statement.

ANSI Merge Source

ansi-merge-source ::= ( merge-source-keyspace | merge-source-subquery | merge-source-expr )
                      ansi-join-hints?

The merge source is the recordset that you want to merge with the merge target. It can be a keyspace reference, a subquery, or a generic expression.

merge-source-keyspace	ANSI Merge Keyspace
merge-source-subquery	ANSI Merge Subquery
merge-source-expr	ANSI Merge Expression
ansi-join-hints	ANSI Merge Source Hints

ANSI Merge Keyspace

merge-source-keyspace ::= keyspace-ref ( 'AS'? alias )?

keyspace-ref	Keyspace Reference
alias	AS Alias

Keyspace Reference

keyspace-ref ::= keyspace-path | keyspace-partial

keyspace-path ::= ( namespace ':' )? bucket ( '.' scope '.' collection )?

keyspace-partial ::= collection

Keyspace reference for the merge source. For details, refer to Keyspace Reference.

AS Alias

Assigns another name to the keyspace reference. For details, refer to AS Clause.

Assigning an alias to the keyspace reference is optional. If you assign an alias to the keyspace reference, the AS keyword may be omitted.

ANSI Merge Subquery

merge-source-subquery ::= subquery-expr 'AS'? alias

subquery-expr	Subquery Expression
alias	AS Alias

Subquery Expression

subquery-expr ::= '(' select ')'

Use parentheses to specify a subquery for the merge source. For details, refer to Subqueries.

AS Alias

Assigns another name to the subquery. For details, refer to AS Clause.

You must assign an alias to a subquery on the merge source. However, when you assign an alias to the subquery, the AS keyword may be omitted.

ANSI Merge Expression

merge-source-expr ::= expr ( 'AS'? alias )?

expr	A SQL++ expression generating JSON documents or objects for the merge source.
alias	AS Alias

AS Alias

Assigns another name to the generic expression. For details, refer to AS Clause.

Assigning an alias to the generic expression is optional. If you assign an alias to the generic expression, the AS keyword may be omitted.

ANSI Merge Source Hints

You can specify ANSI join hints (USE HASH or USE NL) on the source of an ANSI merge. For details, refer to ANSI JOIN Hints.

If the merge source is a keyspace, you can also specify a USE KEYS or USE INDEX hint on the merge source. For details, refer to Multiple Hints.

If the merge action is update or delete, you can specify any of the join methods: USE HASH(BUILD), USE HASH(PROBE), or USE NL.

If the merge action is insert, the only join methods you can specify are USE HASH(PROBE) or USE NL. In this case, if you specify USE HASH(BUILD), the join method will default to USE NL.

The ANSI join hint is optional. If omitted, the default hint is USE NL.

If you are using a nested-loop join, i.e. USE NL is specified or no join hint is specified, the target keyspace reference must have an appropriate secondary index defined for the join to work. If such an index cannot be found an error will be returned.

ANSI Merge Predicate

ansi-merge-predicate ::= 'ON' expr

The merge predicate enables you to specify an ANSI join between the merge source and the merge target.

expr	Boolean expression representing the join condition. This expression may contain fields, constant expressions, or any complex SQL++ expression.

ANSI Merge Actions

ansi-merge-actions ::= merge-update? merge-delete? ansi-merge-insert?

The merge actions enable you to specify insert, update, and delete actions on the target keyspace, based on a match or no match in the join.

merge-update	ANSI Merge Update
merge-delete	ANSI Merge Delete
ansi-merge-insert	ANSI Merge Insert

ANSI Merge Update

merge-update ::= 'WHEN' 'MATCHED' 'THEN' 'UPDATE' set-clause? unset-clause? where-clause?

Updates a document that already exists with updated values.

set-clause	SET Clause
unset-clause	UNSET Clause
where-clause	WHERE Clause

SET Clause

set-clause ::= 'SET' ( meta '=' expiration | path '=' expr update-for? )
               ( ',' ( meta '=' expiration | path '=' expr update-for? ) )*

Specifies the value for an attribute to be changed. Also enables you to set the expiration of the document. For more details, refer to SET Clause.

update-for

FOR Clause

UNSET Clause

unset-clause ::= 'UNSET' path update-for? (',' path update-for?)*

Removes a specified attribute from the document. For more details, refer to UNSET Clause.

update-for

FOR Clause

update-for ::= ('FOR' (name-var ':')? var ('IN' | 'WITHIN') path
               (','   (name-var ':')? var ('IN' | 'WITHIN') path)* )+
               ('WHEN' cond)? 'END'

path ::= identifier ( '[' expr ']' )* ( '.' identifier ( '[' expr ']' )* )*

Iterates over a nested array to SET or UNSET the given attribute for every matching element in the array. For more details, refer to FOR Clause.

WHERE Clause

where-clause ::= 'WHERE' cond

Optionally specifies a condition that must be met for data to be updated. For more details, refer to WHERE Clause.

ANSI Merge Delete

merge-delete ::= 'WHEN' 'MATCHED' 'THEN' 'DELETE' where-clause?

Removes the specified document from the keyspace.

where-clause

WHERE Clause

where-clause ::= 'WHERE' cond

Optionally specifies a condition that must be met for data to be deleted. For more details, refer to WHERE Clause.

ANSI Merge Insert

ansi-merge-insert ::= 'WHEN' 'NOT' 'MATCHED' 'THEN' 'INSERT' '(' 'KEY'? key
                      ( ',' 'VALUE'? value )? ( ',' 'OPTIONS'? options )? ')' where-clause?

Inserts a new document into the keyspace. Use parentheses to specify the key and value for the inserted document, separated by a comma.

Use the UUID() function to generate a random, unique document key.

key	An expression specifying the key for the inserted document. The `KEY` keyword may be omitted. If it is omitted, the `VALUE` keyword must be omitted also.
value	[Optional] An expression specifying the value for the inserted document. If the value is omitted, an empty document is inserted. The `VALUE` keyword may be omitted. If it is omitted, the `KEY` keyword must be omitted also.
options	[Optional] An object representing the metadata to be set for the inserted document. Only the `expiration` attribute has any effect; any other attributes are ignored. expiration An integer, or an expression resolving to an integer, representing the document expiration in seconds. If the document expiration is not specified, it defaults to `0`, meaning the document expiration is the same as the bucket or collection expiration. The `OPTIONS` keyword may be omitted. If it is omitted, the `KEY` and `VALUE` keywords must be omitted also.
where-clause	WHERE Clause

WHERE Clause

where-clause ::= 'WHERE' cond

Optionally specifies a condition that must be met for data to be inserted. For more details, refer to WHERE clause.

Lookup Merge

lookup-merge ::= target-keyspace 'USING' lookup-merge-source lookup-merge-predicate
                 lookup-merge-actions

target-keyspace	Lookup Merge Target
lookup-merge-source	Lookup Merge Source
lookup-merge-predicate	Lookup Merge Predicate
lookup-merge-actions	Lookup Merge Actions

Lookup Merge Target

Keyspace reference for the merge target. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Target.

Lookup Merge Source

lookup-merge-source ::= merge-source-keyspace use-clause? |
                        merge-source-subquery |
                        merge-source-expr

The merge source is the recordset that you want to merge with the merge target. It can be a keyspace reference, a subquery, or a generic expression.

merge-source-keyspace	Lookup Merge Keyspace
use-clause	Lookup Merge Source Hint
merge-source-subquery	Lookup Merge Subquery
merge-source-expression	Lookup Merge Expression

Lookup Merge Keyspace

Keyspace reference for the merge source. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Keyspace.

Lookup Merge Source Hint

If the merge source is a keyspace, you can specify a USE KEYS or USE INDEX hint on the merge source. For details, refer to USE clause.

Lookup Merge Subquery

Specifies a subquery for the merge source. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Subquery.

Lookup Merge Expression

Specifies a generic expression for the merge source. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Expression.

Lookup Merge Predicate

lookup-merge-predicate ::= 'ON' 'PRIMARY'? 'KEY' expr

The merge predicate produces a document key for the target of the lookup merge.

expr	[Required] String or expression representing the primary key of the documents for the target keyspace.

Lookup Merge Actions

lookup-merge-actions ::= merge-update? merge-delete? lookup-merge-insert?

The merge actions enable you to specify insert, update, and delete actions on the target keyspace, based on a match or no match in the join.

merge-update	Lookup Merge Update
merge-delete	Lookup Merge Delete
lookup-merge-insert	Lookup Merge Insert

Lookup Merge Update

Updates a document that already exists with updated values. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Update.

Lookup Merge Delete

Removes the specified document from the keyspace. The syntax is the same as for an ANSI merge. Refer to ANSI Merge Delete for details.

Lookup Merge Insert

lookup-merge-insert ::= 'WHEN' 'NOT' 'MATCHED' 'THEN' 'INSERT' expr where-clause?

Inserts a new document into the keyspace. The key specified in the Lookup Merge Predicate is used as the key for the newly inserted document.

expr	An expression specifying the value for the inserted document.
where-clause	WHERE Clause

The Lookup Merge Insert syntax does not enable you to specify the document expiration. If you need to specify the document expiration, rewrite the query using the ANSI Merge Insert syntax.

WHERE Clause

where-clause ::= 'WHERE' cond

Optionally specifies a condition that must be met for data to be inserted. For more details, refer to WHERE clause.

Common Clauses

The following clauses are common to both ANSI Merge and Lookup Merge.

LIMIT Clause

limit-clause ::= 'LIMIT' expr

Specifies the minimum number of records to be processed. For more details, refer to LIMIT Clause.

RETURNING Clause

returning-clause ::= 'RETURNING' (result-expr (',' result-expr)* |
                    ('RAW' | 'ELEMENT' | 'VALUE') expr)

Specifies the information to be returned by the operation as a query result. For more details, refer to RETURNING Clause.

Examples

To try the examples in this section, set the query context to the inventory scope in the travel sample dataset. For more information, see Query Context.

Please note that the examples below will alter the data in your sample buckets. To restore your sample data, remove and reinstall the travel-sample bucket. Refer to Import Sample Data for details.

Example 1. ANSI merge with expression source

This example updates the vacancy field based on the source expression.

MERGE INTO hotel t
USING [
  {"id":"21728", "vacancy": true},
  {"id":"21730", "vacancy": true}
] source
ON meta(t).id = "hotel_" || source.id
WHEN MATCHED THEN
  UPDATE SET t.old_vacancy = t.vacancy,
             t.vacancy = source.vacancy
RETURNING meta(t).id, t.old_vacancy, t.vacancy;

Example 2. ANSI merge with keyspace source

This example finds all BA routes whose source airport is in France. If any flights are using equipment 319, they are updated to use 797. If any flights are using equipment 757, they are deleted.

MERGE INTO route
USING airport
ON route.sourceairport = airport.faa
WHEN MATCHED THEN UPDATE
  SET route.old_equipment = route.equipment,
      route.equipment = "797",
      route.updated = true
  WHERE airport.country = "France"
    AND route.airline = "BA"
    AND CONTAINS(route.equipment, "319")
WHEN MATCHED THEN DELETE
  WHERE airport.country = "France"
    AND route.airline = "BA"
    AND CONTAINS(route.equipment, "757")
RETURNING route.old_equipment, route.equipment, airport.faa;

Example 3. ANSI merge with updates and inserts

This example compares a source set of airport data with the airport keyspace data. If the airport already exists in the airport keyspace, the record is updated. If the airport does not exist in the airport keyspace, a new record is created.

MERGE INTO airport AS target
USING [
  {"iata":"DSA", "name": "Doncaster Sheffield Airport"},
  {"iata":"VLY", "name": "Anglesey Airport / Maes Awyr Môn"}
] AS source
ON target.faa = source.iata
WHEN MATCHED THEN
  UPDATE SET target.old_name = target.airportname,
             target.airportname = source.name,
             target.updated = true
WHEN NOT MATCHED THEN
  INSERT (KEY UUID(),
          VALUE {"faa": source.iata,
                 "airportname": source.name,
                 "type": "airport",
                 "inserted": true} )
RETURNING *;

Example 4. ANSI merge with expiration

This example compares a source set of airport data with the airport keyspace data. If the airport already exists in the airport keyspace, the record is updated, and the existing document expiration is preserved. If the airport does not exist in the airport keyspace, a new record is created with an expiration of one week.

MERGE INTO airport AS target
USING [
  {"iata":"DSA", "name": "Doncaster Sheffield Airport"},
  {"iata":"VLY", "name": "Anglesey Airport / Maes Awyr Môn"}
] AS source
ON target.faa = source.iata
WHEN MATCHED THEN
  UPDATE SET target.old_name = target.airportname,
             target.airportname = source.name,
             target.updated = true,
             meta(target).expiration = meta(target).expiration
WHEN NOT MATCHED THEN
  INSERT (KEY UUID(),
          VALUE {"faa": source.iata,
                 "airportname": source.name,
                 "type": "airport",
                 "inserted": true},
          OPTIONS {"expiration": 7*24*60*60} );

Note that it is possible to preserve the document expiration using the request-level preserve_expiry parameter.

Example 5. Lookup merge with expression source

Lookup merge version of Example 1.

MERGE INTO hotel t
USING [
  {"id":"21728", "vacancy": true},
  {"id":"21730", "vacancy": true}
] source
ON KEY "hotel_"|| source.id
WHEN MATCHED THEN
  UPDATE SET t.old_vacancy = t.vacancy, t.vacancy = source.vacancy
RETURNING meta(t).id, t.old_vacancy, t.vacancy;

Example 6. Lookup merge with keyspace source

The following statement updates product based on orders.

MERGE INTO product p USING orders o ON KEY o.productId
WHEN MATCHED THEN
  UPDATE SET p.lastSaleDate = o.orderDate
WHEN MATCHED THEN
  DELETE WHERE p.inventoryCount  <= 0;

Example 7. Lookup merge with updates and inserts

The following statement merges two datasets containing employee information. It then updates all_empts on match with emps_deptb and inserts when there is no match.

MERGE INTO all_empts a USING emps_deptb b ON KEY b.empId
WHEN MATCHED THEN
  UPDATE SET a.depts = a.depts + 1
  a.title = b.title || ", " || b.title
WHEN NOT MATCHED THEN
  INSERT { "name": b.name,
           "title": b.title,
           "depts": b.depts,
           "empId": b.empId,
           "dob": b.dob };