如果ID不存在，则在表2上执行MySQL UPDATE表1和INSERT

Question

I have a left join query that shows all the fields from a primary table (tblMarkers) and the values from a second table (tblLocations) where there is matching record. tblLocations does not have a record for every id in tblMarkers

$query ="SELECT `tblMarkers`.*,`tblLocation`.*,`tblLocation`.`ID` AS `markerID`
FROM
   `tblMarkers`
 LEFT JOIN `tblLocation` ON `tblMarkers`.`ID` = `tblLocation`.`ID`
WHERE
`tblMarkers`.`ID` = $id";

I am comfortable with using UPDATE to update the tblMarkers fields but how do I update or INSERT a record into tblLocations if the record does not exist yet in tblLocations.

Also, how do I lock the record I ma working on to prevent someone else from doing an update at the same time?

Can I also use UPDATE tblMarkers * or do I have to list every field in the UPDATE statement?

Answer 1

Unfortunately you might have to implement some validation in your outside script. There is an IF statement in SQL, but I'm not sure if you can trigger different commands based on it's outcome.

Locking

In terms of locking, you have 2 options. for MyISAM tables, you can only lock the entire table using http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html

LOCK TABLE users;

For InnoDB tables, there is no explicit 'lock' for single rows, however you can use transactions, to get exclusive rights during the operation. http://dev.mysql.com/doc/refman/5.0/en/innodb-locks-set.html

Update

There might be some shorthand notation, but I think you have to list every field in your query. Alternatively, you can always read the entire row, delete it and insert again using shorthand INSERT query. It all depends on how many fields you've got.