UPDATE statement: The statement _ MySQL

UPDATE statement: UPDATE the fields in one table to the statement bitsCN.com in another table.

UPDATE statement: The statement used to UPDATE fields in one table to fields in another table.

In a modification to the score query system, a table is changed and a field is added to a table. now, you need to copy the corresponding ID of another table, because such SQL operations are not often used, I even thought of writing a loop to process them. However, I thought that SQL should be able to implement such a function. I checked the manual and it was really simple. there was a syntax for updating... from. Example:

Table

Id subject_id

1 null

2 null

3 null

4 null

5 null

6 null

Table B

Sb_id st_id

5 1

2 2

5 3

5 4

2 5

2 6

The SQL statement is as follows:

1

UPDATEASETA. subject_id = B. sb_idFROMBWHEREB.student_id = A. id

Update: the preceding statement is only applicable to mssql server and the following statement should be used in mysql:

1

UPDATEA, BSETA. subject_id = B. sb_idWHEREB.student_id = A. id

Example 2:

MYSQL is

Update table2 B, (select B. area_id as arid, sum (a. user_amount) as bcount

From table1 a, table2 B

Where a. user_area = B. area_id

Group by arid) c

Set B. count = c. bcount

Where B. area_id = c. arid;

I also installed a MYSQL test and the test passed.

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