https://www.cnblogs.com/digde.
reads the above article, which says:
the following types of where conditions and their combinations may use the index union merge algorithm:
1) the condition uses all fields in the composite index or left prefix fields (also applicable to single-field indexes)
the composite index here refers to the federated index, but I think if there is a federated index, it should not go through index merging, right?
$selectTip = $pdo->query("SELECT * FROM `tips_rate` WHERE `tip_id` = ".$row[ id ]." " ); $selecttotal = mysqli_num_rows($selectTip); $rate = $pdo->query("SELEC...
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like this SELECT * FROM material WHERE {key:value} limit 1 ...
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Table structure ...
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