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39b019574a
* Feature #7675 - EXPLAIN statement and RDB$SQL package. * Change ObjectsArray::back() to match STL semantics and add front() method. * Fix indentation problem. * Add OBJECT_TYPE column. * Add CARDINALITY column. * Add conversion from bid to ISC_QUAD. * Replace fb_assert by static_assert. * Change ACCESS_PATH output parameter to blob. * Improve docs.
47 lines
1.5 KiB
Markdown
47 lines
1.5 KiB
Markdown
# RDB$SQL package (FB 6.0)
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`RDB$SQL` is a package with utility routines to work with dynamic SQL.
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## Procedure `EXPLAIN`
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`RDB$SQL.EXPLAIN` returns tabular information of a query's plan, without execute the query.
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Since `SQL` text generally is multi-line string and have quotes, you may use `<alternate string literal>`
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(strings prefixed by `Q`) as a way to make escape easy.
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Input parameters:
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- `SQL` type `BLOB SUB_TYPE TEXT CHARACTER SET UTF8 NOT NULL` - query statement
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Output parameters:
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- `PLAN_LINE` type `INTEGER NOT NULL` - plan's line order
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- `RECORD_SOURCE_ID` type `BIGINT NOT NULL` - record source id
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- `PARENT_RECORD_SOURCE_ID` type `BIGINT` - parent record source id
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- `LEVEL` type `INTEGER NOT NULL` - indentation level (may have gaps in relation to parent's level)
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- `PACKAGE_NAME` type `RDB$PACKAGE_NAME` - package name of a stored procedure
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- `OBJECT_NAME` type `RDB$RELATION_NAME` - object (table, procedure) name
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- `ALIAS` type `RDB$RELATION_NAME` - alias name
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- `RECORD_LENGTH` type `INTEGER` - record length for the record source
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- `KEY_LENGTH` type `INTEGER` - key length for the record source
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- `ACCESS_PATH` type `VARCHAR(255) CHARACTER SET UTF8 NOT NULL` - friendly plan description
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```
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select *
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from rdb$sql.explain('select * from employees where id = ?');
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```
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```
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select *
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from rdb$sql.explain(q'{
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select *
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from (
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select name from employees
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union all
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select name from customers
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)
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where name = ?
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}');
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```
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# Authors
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- Adriano dos Santos Fernandes
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