diff options
| -rw-r--r-- | doc/src/sgml/ref/alter_table.sgml | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml index 5c0735e08a8..e610cbbc0ec 100644 --- a/doc/src/sgml/ref/alter_table.sgml +++ b/doc/src/sgml/ref/alter_table.sgml @@ -1366,7 +1366,13 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM existing column, if the <literal>USING</literal> clause does not change the column contents and the old type is either binary coercible to the new type or an unconstrained domain over the new type, a table rewrite is not - needed; but any indexes on the affected columns must still be rebuilt. + needed. However, indexes must always be rebuilt unless the system can + verify that the new index would be logically equivalent to the existing + one. For example, if the collation for a column has been changed an index + rebuild is always required because the new sort order might be different. + However, in the absence of a collation change, a column can be changed + from <type>text</type> to <type>varchar</type> (or vice versa) without + rebuilding the indexes because these data types sort identically. Table and/or index rebuilds may take a significant amount of time for a large table; and will temporarily require as much as double the disk space. |