java - 这一条sql哪里错了呀？

Question

SELECT a.*,b.custom_name FROM zqwl_receipt a , zqwl_custom b LEFT JOIN b WHERE a.id= b.id

Answer 1

The usage of

left join is generally to query the main table first and then join other tables, such as

select a.*, b.custom_name from zqwl_receipt a
left join zqwl_custom b on a.id = b.id

If you want to combine the query results of two tables a and b and then perform a related search, you may be able to use a subquery

select * from (
  select a.*, b.custom_name from zqwl_receipt a, zqwl_custom b where a.id = b.id
) t
left join zqwl_custom t2 on t2.id = t.id

But if you write such a statement, you’d better think about the design issues of tables a and b,
or this is completely unnecessary

Answer 2

SELECT zqwl_receipt.*,zqwl_custom.custom_name from xxx LEFT JOIN xxx

Answer 3

from a left join b on a.id=b.id

Answer 4

Where did your FROM go

Answer 5

There is no from table
There is no on to filter the relationship between these two tables.

SELECT zqwl_receipt.*,zqwl_custom.custom_name from zqwl_receipt LEFT JOIN zqwl_custom on zqwl_custom.field= zqwl_receipt.field WHERE zqwl_receipt.id= zqwl_custom.id

Answer 6

Basic syntax errors