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VolkerK
VolkerK
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mysql_query() transfers all result records from the MySQL into the php pcrocess before it returns (unlike mysql_unbufferd_query()). That alone would make the mysql_num_rows() version slower.

Furthermore for some engines (like MyISAM) MySQL can serve a Count(*) request from the index of the table without hitting the actual datawithout hitting the actual data. A SELECT * FROM foo on the other hand results in a full table scan and MySQL has to read every single dataset.

mysql_query() transfers all result records from the MySQL into the php pcrocess before it returns (unlike mysql_unbufferd_query()). That alone would make the mysql_num_rows() version slower.

Furthermore for some engines (like MyISAM) MySQL can serve a Count(*) request from the index of the table without hitting the actual data. A SELECT * FROM foo on the other hand results in a full table scan and MySQL has to read every single dataset.

mysql_query() transfers all result records from the MySQL into the php pcrocess before it returns (unlike mysql_unbufferd_query()). That alone would make the mysql_num_rows() version slower.

Furthermore for some engines (like MyISAM) MySQL can serve a Count(*) request from the index of the table without hitting the actual data. A SELECT * FROM foo on the other hand results in a full table scan and MySQL has to read every single dataset.

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VolkerK
VolkerK
  • 95.9k
  • 20
  • 165
  • 230

mysql_query() transfers all result records from the MySQL into the php pcrocess before it returns (unlike mysql_unbufferd_query()). That alone would make the mysql_num_rows() version slower.

Furthermore for some engines (like MyISAM) MySQL can serve a Count(*) request from the index of the table without hitting the actual data. A SELECT * FROM foo on the other hand results in a full table scan and MySQL has to read every single dataset.