SQL遍历表中的记录

Question

I have a table called master, the primary key is account_num. Each account number has an account_type (single character). I need to do the following:

1. find all accounts with a type of A or B.
2. store that account number in a new table called year_end_close along with a time stamp of when that transaction takes place
3. set all accounts in master with a type of A to C, and all accounts with a type of B to D

What's the best way to handle this in SQL? While loop? Case statement? Cursor? Any help is appreciated. The table has about 17,000 rows.

Answer 1

You shouldn't need to use a cursor/loop to do something like this. When writing SQL, always try to look for a set-based solution first. I would recommend a CASE statement, which was one of the options you mentioned.

Try this:

BEGIN TRAN;

SELECT account_num, CURRENT_TIMESTAMP
INTO year_end_close
FROM dbo.master
WHERE account_type IN ('a','b');

UPDATE dbo.master
SET account_type = CASE account_type
                     WHEN 'a' THEN 'c'
                     WHEN 'b' THEN 'd'
                     ELSE account_type
                     END
WHERE account_type IN ('a','b');

COMMIT TRAN;

Answer 2

Are you searching for something like this? (Replace the 'PRINT' statements for your actual SQL statements)

DECLARE @MasterTable TABLE
(
  account_num int,
  account_type varchar(1)
)
INSERT INTO @MasterTable VALUES (1, 'A')
INSERT INTO @MasterTable VALUES (2, 'A')
INSERT INTO @MasterTable VALUES (3, 'B')
INSERT INTO @MasterTable VALUES (4, 'B')
INSERT INTO @MasterTable VALUES (5, 'C')
INSERT INTO @MasterTable VALUES (6, 'C')

DECLARE @account_num int
DECLARE @account_type varchar(1)
DECLARE @switch_type varchar(1)

DECLARE db_cursor CURSOR FOR  
SELECT account_num, account_type 
FROM @MasterTable
WHERE account_type IN ('A', 'B')  

OPEN db_cursor   
FETCH NEXT FROM db_cursor INTO @account_num, @account_type  

WHILE @@FETCH_STATUS = 0   
BEGIN   
    IF @account_type = 'A'
        SET @switch_type = 'C'
    ELSE
        SET @switch_type = 'D'

    PRINT 'INSERT year_end_close (account_num, timestampfield) VALUES (' + CAST(@account_num AS VARCHAR) + ', GETDATE())'
    PRINT 'UPDATE @MasterTable SET account_type = ' + @switch_type + ' WHERE account_num = ' + CAST(@account_num AS VARCHAR)
FETCH NEXT FROM db_cursor INTO @account_num, @account_type   
END   

CLOSE db_cursor   
DEALLOCATE db_cursor