动态查询引用三级

.sql

EXECUTE 'UPDATE tbl SET '
        || quote_ident(colname) -- 
        || ' = '
        || quote_nullable(newvalue)
        || ' WHERE key = '
        || quote_literal(keyvalue);

EXECUTE format('UPDATE tbl SET %I = %L '
   'WHERE key = %L', colname, newvalue, keyvalue);
   
   %I is equivalent to quote_ident, and %L is equivalent to quote_nullable. 
   The format function can be used in conjunction with the USING clause:
   
   EXECUTE format('UPDATE tbl SET %I = $1 WHERE key = $2', colname)
   USING newvalue, keyvalue;