我有一个性能很差的查询(我继承的),我不太确定如何优化它......据我所知,它将第二列的值设置为第一列的值加上一个值另一个表,其中找到了关系。
update table1 set
col2 = col1 || coalesce ((
select table2.the_column_wanted from table2 where table2.fk = table1.pk and
table2.flag = 'Y'))
where flag = 'Y' and pk in ( select distinct fk from table2 );