> I come from the Oracle world and am trying to convert some queries to > PostgreSQL syntax. One of these queries is a MERGE statement, which I > converted into an UPDATE SET FROM WHERE construct. In the original > query I use the pseudo column ROWID to match a source row with a > target row. > > In the PostgreSQL version I use the column ctid for this. The above query > becomes: > > *UPDATE*test_large d > *SET* grp = s.grp > *FROM* (*SELECT* ctid, test_large.* > *FROM* test_large > *WHERE* grp = 1) s > *WHERE* d.ctid = s.ctid;
Why don't you join on the primary key column? The ctid comparison is typically quite slow. Thomas
