因此如果要对a表过滤需要把条件写在where里面，要对b表过滤需要把调教写在b表的子查询里面，至于[ON]只是用来控制显示的。
-EOF-
Left Join(三)
.02 rows=1 width=7)
Rows in: Avg 1.0 rows x 2 workers. Max 1 rows (seg42) with 0.103 ms to end, start offset by 12 ms.
-> Seq Scan on tgt2 b (cost=0.00..2.02 rows=1 width=7)
Rows out: Avg 1.0 rows x 2 workers. Max 1 rows (seg42) with 0.074 ms to first row, 0.076 ms to end, start offset by 12 ms.
Slice statistics:
(slice0) Executor memory: 332K bytes.
(slice1) Executor memory: 569K bytes avg x 64 workers, 4337K bytes max (seg42). Work_mem: 58K bytes max.
Statement statistics:
Memory used: 128000K bytes
Total runtime: 436.384 ms
(27 rows)