Hi all,
I have two tables containing the following:
table1:
+----------------------------------+--------------------+
| UNID | DATE |
+----------------------------------+--------------------+
| 08294D5D0F9ABE6D46663300BDB6521C | 2001-09-09 02:00:30|
| FF4210F70A19D36856663300BDB6521C | NULL |
| FB499B109E1C6E1466663300BDB6521C | NULL |
| 9429E5EC91F7508676663300BDB6521C | NULL |
| 578313DA1378F96E86663300BDB6521C | 2001-10-21 02:00:40|
... etc .... etc ....
table2:
+-----+----------------------------------+-------------------+----------------------------------+
| ID | PO_UNID | CONTENT |
PO_DOCID |
+-----+----------------------------------+-------------------+----------------------------------+
| 519 | 08294D5D0F9ABE6D46663300BDB6521C | on |
D6EBA9F0D5D49280C1256BDB00336664 |
+-----+----------------------------------+-------------------+----------------------------------+
| 520 | 08294D5D0F9ABE6D46663300BDB6521C | off |
DFAEFFFWE33771FSDSF428DSF3559999 |
+-----+----------------------------------+-------------------+----------------------------------+
My problem is that the following query results in several thousand tupels:
SELECT UNID FROM TABLE1 WHERE DATE IS NULL;
Therefore I use:
SELECT UNID FROM TABLE1 WHERE DATE IS NULL LIMIT 1;
Now I want to do the following:
SELECT UNID FROM TABLE1 WHERE DATE IS NULL LIMIT 1;
SELECT CONTENT FROM TABLE2 WHERE PO_UNID='<RESULT PREVIOUS QUERY>'
Instead of writing two queries this could be written as:
mysql> select 0.UNID, c.CONTENT
-> from table1 o, table2 c
-> where o.DATE IS NULL
-> and o.UNID = c.PO_UNID
-> LIMIT 1;
This results query gives me the right result but it's execution time
takes allmost 6 times longer then the two seperate queries.
I'm planning to make these queries in a JAVA program (Using the
JDBC-bridge). Which variation is smarter? Using the 2 queries, or using
the second variation met the join?
Any help would be greatly appreciated.
Many Thanks,
Harm de Laat
Informatiefabriek
The Netherlands
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