Question

I am making a daily counter for a blog and I have problem with this query :

IF EXISTS SELECT * FROM tableA WHERE blog_id=1
    UPDATE FROM tableA SET c=c+'1' WHERE blog_id='1' AND c_date=NOW()
ELSE
    INSERT INTO FROM tableA VALUES (blog_id,c,c_date) VALUES (1,1,now())

its showing following error :

1064 – You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use

near ‘IF EXISTS SELECT * FROM tableA WHERE blog_id=1 UPDATE FROM
tableA SET c=c+” at line 1

My table entries should look like this :
id , blod_id , c , c_date
1 , 1001, 66 , 2011-11-11 
2 , 1001, 160 , 2011-11-12
3 , 1002, 200 , 2011-11-12
4 , 1003, 33 , 2011-11-12

Answer 1

I suspect you’re lokoing for the insert into on duplicate key update syntax

From the manual:

12.2.5.3. INSERT … ON DUPLICATE KEY UPDATE Syntax

If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that would cause a
duplicate value in a UNIQUE index or PRIMARY KEY, an UPDATE of the old
row is performed.

http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html

Your query should look more like the following example:

INSERT INTO tableA (blog_id,c,c_date) VALUES (1,1,now()) ON DUPLICATE KEY UPDATE `c` = `c`+1, `c_date` = NOW()

You need to have a UNIQUE key or a PRIMARY KEY for this to work.

ALTER TABLE  `table` ADD PRIMARY KEY (  `id` )

---

Based on your table example you could add a primary key to the id column or add a unique composite index on the (c_date, blog_id) fields

ALTER TABLE  `table` ADD UNIQUE (
blog_id ,
c_date
);

and use this:

INSERT INTO tableA (blog_id, c, c_date) 
  VALUES (1, 1, NOW()) 
ON DUPLICATE KEY UPDATE 
  c = c + 1                --- update only `c`, not any part of the unique key