mysql select within select

The most common operation of database is "plug, check, delete, change". In the previous log, I introduced the MySQL inserts INSERT statement, also introduced the update UPDATE statement for everyone, as well as deletes the statement delete and the

MySQL functions and Usage examples String functions ASCII (str)Returns the ASCII value of the first character of the string 'str' (0 is returned when 'str' is an empty string)Mysql> select ASCII ('2 ');-> 50Mysql> select ASCII (2 );-> 50Mysql>

String functionsASCII (str)Returns the ASCII value of the first character of the string str (str is empty when the string returns 0)Mysql> Select ASCII (' 2 ');50Mysql> Select ASCII (2);50Mysql> Select ASCII (' dete ');100ORD (str)If the string str

Select the MYSQL column type bitsCN.com Select the MYSQL column type When creating a table, how does one determine which types to use? This section describes the factors that should be taken into account before making a decision. The most "common"

String function string comparison function if the result length is greater than the maximum value of the max_allowed_packet system variable, the return value of the string value function is NULL. See section 7.5.2 "Adjust server Parameters ". String

Generally, the entire string is used as the operation object, for example: search for a substring in a substring, obtain a substring, insert a substring at a certain position in the substring, and delete a substring. Generally, the entire string is

Select Column1+10 as c1,c1+10 as C2 from table1;Want to achieve the above effect, the result in MySQL inside error, the hint can not find C1 this column;-Different databases are not the sameIt is not generally supported to continue using aliases in

String functionsstring comparison functionsIf the length of the result is greater than the maximum value of the Max_allowed_packet system variable, the return value of the string value function is null. See section 7.5.2, "Tuning server parameters."

In general, to make a slow select... where faster, you should first check whether an index can be added. References between different tables are usually completed through indexes. You can use the explain statement to determine which indexes the

In general, to make a slower select ... where it is faster, you should first check to see if you can add an index. References between different tables are usually done by index. You can use the explain statement to determine which indexes the SELECT