It does not have to use an index because you have not supplied row
restriction criteria. An index is being used to relate the two tables.
-----Original Message-----
From: Daniel Cummings
To: [EMAIL PROTECTED]
Sent: 5/24/04 6:05 PM
Subject: Understanding Explain in 4.1
These are two simple stock quotes tables that contain a symbol and a
close
amount.
Explain
Select Monday.Symbol, Friday.Close, Monday.Close
From Monday Force Index(Symbol) Inner Join Friday Force Index(Symbol)
ON
Monday.Symbol = Friday.Symbol
Symbol is a VarChar(20) in both tables.
There is an index on Symbol for both of these table.
The resultant Explain shows that
+----------+------+-----------------+------------+---------+------------
----
---+-----------+-------------+
| table | type | possible_keys | key | key_len |
ref
| rows | Extra |
+----------+------+-----------------+------------+---------+------------
----
---+-----------+-------------+
| Monday | All | Symbol | [Null] | [Null] |
[Null] | 60134 | |
+----------+------+-----------------+------------+---------+------------
----
---+-----------+-------------+
| Friday | ref | Symbol | Symbol | 21 |
Monday.Symbol | 1 | where used |
+----------+------+-----------------+------------+---------+------------
----
---+-----------+-------------+
Why aren't both using the Symbol key?
Why isn't the Force Index working?
TIA
Dan
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