从所有表中具有相同主键的多个表中获取数据

Question

I have 4 tables all with the same primary key with structure like :

table_1 : u_id | col1 | col2    

table_2 : u_id | col3 | col4     

table_3 : u_id | col5 | col6    

table_4 : u_id | col7 |  col8

I want to fetch the data of "col1", "col4", "col6" and "col7" on the basis of the value of u_id .

Values of u_id are same in every table.

For eg. if u_id='8' , then fetch all the specified column values where u_id='8' .

I am not using joins correctly, i guess.

Thanks.

Answer 1

This should be pretty straight forward. Use INNER JOIN

SELECT  a.col1, b.col4, c.col6, d.col7
FROM    table1 a
        INNER JOIN table2 b
            ON a.u_id = b.uid
        INNER JOIN table3 c
            ON a.u_id = c.uid
        INNER JOIN table4 d
            ON a.u_id = d.uid
WHERE   a.u_ID = 8

To learn more about joins, please see the article below.

• Visual Representation of SQL Joins

Answer 2

SELECT 
table_1.col1, 
table_2.col4, 
table_3.col6, 
table_4.col7 
FROM
table_1,
table_2,
table_3,
table_4
WHERE
table_1.u_id = '8' AND
table_1.u_id = table_2.u_id AND
table_1.u_id = table_3.u_id AND
table_1.u_id = table_4.u_id