Updating database tables

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Special semantics regarding UNION can also be employed to allow “recursive” queries, where a SELECT statement can draw upon the set of rows that have previously been selected.

CTEs can also be applied to DML constructs UPDATE, INSERT and DELETE on some databases, both as a source of CTE rows when combined with RETURNING, as well as a consumer of CTE rows. This is used to support backend-specific prefix keywords such as those provided by My SQL.

Subclasses should override the default behavior, which is a straight identity comparison.

**kw are arguments consumed by subclass compare() methods and may be used to modify the criteria for comparison. Common table expressions are a SQL standard whereby SELECT statements can draw upon secondary statements specified along with the primary statement, using a clause called “WITH”.

'wp-admin/includes/upgrade.php' ); db Delta( $sql ); to get the character set and collation.

But neither of those options is very satisfactory, since a user could easily forget to run the install script or mess up the query (and they might not have php My Admin available).

The use case for ad-hoc addition of argument names is typically for end-user code that is also using a custom compilation scheme which consumes the additional arguments.

Compare this Clause Element to the given Clause Element.

Thus to assure consistent data, it appears to be best practice to ensure that your query include an "id column" as the first field.

(When developing custom tables, be sure to make id your first column for this reason!

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