MySQL Addendum 1

Recently I summarized some operations that are easy to ignore in MySQL, and some of them are quite good.
1) perror code viewing tool
Recently, it is often found that errors such as error no: in MySQL are often found during MySQL import and export, but if you need to know where the error is,
In fact, MySQL has a built-in tool perror, for example, this can be used.
Perror 30
The error message of code 30 is displayed.

2) mysqlcheck Tool
Parameters include-C (check),-R (repair)-A (analysis)-O (optimization)
For example, mysqlcheck-u root-P table name-C

3) myisampack Tool
Note: This tool can compress tables, but the compressed tables can only be read-only and reduce the space.
Myisampack table name
4 In the MySQL status, you can use the optimize table name to optimize the table. In particular, you can combine the shard space in the table to work only for MyISAM and InnoDB.

5. View MySQL Parameters
You can use show variables to view the configuration of each parameter and the server status. You can use show status to view the status,
However, it is recommended that you use the system variables in phpMyAdmin and other convenient page methods for better viewing.

6 sqlmode Introduction
In my. ini, you can see the following settings
# Set the SQL mode to strict
SQL-mode = "strict_trans_tables, no_auto_create_user, no_engine_substitution"
Enabled by default,
In MySQL 5, the default values are real_as_float, pipes_as_contact, ansi_quotes, gnore_space, and ANSI,
In this mode, values that exceed the length of a field are allowed to be inserted. After the value is inserted, a warning rather than an error is returned. When strict_trans_tables is used,
It is an error and a strict warning is given.

No_auto_create_user <! ---->

Prevent grant from automatically creating new users unless a password is specified.

The following are some introductions in the manual.

All supported modes are described below:

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· Allow_invalid_dates

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Do not check all dates in strict mode. Only check the day between the month and the day between 1 and 12. This is important in Web applications when you get the year, month, and day from three different fields and want to exactly save the content inserted by the user (without date verification. This mode applies to date and datetime columns. It is not suitable for the timestamp column. The timestamp column requires the verification date.

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After the strict mode is enabled, the server requires valid months and days, not only in the range of 1 to 12 and 1 to 31, respectively. For example, '2017-04-31 'is valid when strict mode is disabled, but it is invalid when strict mode is enabled. Allow_invalid_dates should also be enabled to allow the masking of fixed dates in strict mode.

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· Ansi_quotes

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Use 'as an identifier quotation mark ('''). Do not use it as a string quotation mark. In ANSI mode, you can still use ''' to reference the identifier. When ansi_quotes is enabled, you cannot use double quotation marks to reference strings because it is interpreted as an identifier.

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· Error_for_division_by_zero

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In strict mode, if the insert or update process is divided by zero (or mod (x, 0), an error is generated (otherwise it is a warning ). If this mode is not provided, MySQL returns NULL if it is divided by zero. If insert ignore or update ignore is used, MySQL generates a zero division warning, but the operation result is null.

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· High_not_precedence

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The priority of the not operator is that the expression, for example, not a between B and C, is interpreted as not (A between B and C ). In some earlier versions of MySQL, the expression is interpreted as (not a) between B and C. Enable the high_not_precedencesql mode to obtain results with a higher priority.

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mysql> SET sql_mode = ‘’;

mysql> SELECT NOT 1 BETWEEN -5 AND 5;

        -> 0

mysql> SET sql_mode = ‘broken_not’;

mysql> SELECT NOT 1 BETWEEN -5 AND 5;

        -> 1

· Ignore_space

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A space is allowed between the function name and. All function names are considered as saved words. The result is that if you want to access the database, table, or column name that is saved as a word, you must reference it. For example, because there is a user () function, the user table name in the MySQL database and the user column in the table are saved, so you must reference them:

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SELECT "User" FROM mysql."user";

· No_auto_create_user

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Prevent grant from automatically creating new users unless a password is specified.

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· No_auto_value_on_zero

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No_auto_value_on_zero affects the processing of the auto_increment column. Generally, you can insert null or 0 to this column to generate the next serial number. No_auto_value_on_zero disables 0, so only null can generate the next serial number.

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This mode is useful if you save 0 to the auto_increment column of the table. (This Convention is not recommended ). For example, if you useMysqldumpDump the table and reload it. MySQL generates a new serial number when it encounters a value of 0. The contents of the generated table are different from those of the dump table. Enable no_auto_value_on_zero before reloading the dump file to solve this problem.MysqldumpThe output automatically contains the statement that enables no_auto_value_on_zero.

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· No_backslash_escapes

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Disables the backslash ('\') as the exit character in the string. If this mode is enabled, the backslash is a common character.

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· No_dir_in_create

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Ignore all index directory And data directory commands when creating a table. This option is useful for slave replication servers.

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· No_engine_substitution

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If the required storage engine is disabled or not compiled, the storage engine cannot be replaced automatically.

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· No_field_options

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Do not print the MySQL special column option in the output of show create table. This mode is used in portability ModeMysqldump.

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· No_key_options

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Do not print mysql-specific index options in the output of show create table. This mode is used in portability ModeMysqldump.

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· No_table_options

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Do not print the MySQL special table option (such as engine) in the output of show create table ). This mode is used in portability ModeMysqldump.

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· No_unsigned_subtraction

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In a subtraction operation, if an operand has no symbols, do not mark the result as unsigned. Note that the unsigned bigint cannot be 100% used in context. See section 12.8 "cast functions and operators ".

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· No_zero_date

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In strict mode, do not use '2017-00-00 'as a valid date. You can still use the ignore option to insert a zero date. In non-strict mode, this date is acceptable, but a warning is generated.

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· No_zero_in_date

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In strict mode, the date of month or day is not accepted. If the ignore option is used, we insert '2017-00-00 'for a similar date ′. In non-strict mode, this date is acceptable, but a warning is generated.

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· Only_full_group_by

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Do not point the query in the group by section to an unselected column.

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· Pipes_as_concat

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| Is treated as a String concatenation operator (+) (same as Concat (), not as or.

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· Real_as_float

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Treat real as a synonym for float, rather than a synonym for double.

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· Strict_trans_tables

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Enable strict mode for all storage engines. The invalid data value is denied. Detailed descriptions are provided later.

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· Strict_trans_tables

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Enable strict mode for the transaction storage engine, or enable strict mode for the non-transaction storage engine. Detailed descriptions are provided later.

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Strictly control how MySQL processes illegal or lost input values. One value can be invalid for several reasons. For example, the data type is incorrect. It is not suitable for columns or is out of range. If the newly inserted row does not contain a column that does not display the value defined by the default clause, the value is lost.

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When the strict_all_tables or strict_trans_tables mode is enabled for a transaction table, an error occurs if the statement contains an invalid or missing value. The statement is abandoned and rolled.

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For non-transaction tables, if the 1st rows inserted or updated have bad values, the two modes share the same behavior. The statement is abandoned and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value appears in the 2nd or later rows, the result depends on which strict option is enabled:

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· For strict_all_tables, MySQL returns an error and ignores the remaining rows. However, in this case, the previous row has been inserted or updated. This indicates that you can update some data, which may not be what you want. To avoid this, it is best to use a single row statement, because you can give up without changing the table.

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· For strict_trans_tables, MySQL converts invalid values to valid values closest to the column and inserts the adjusted values. If the value is lost, MySQL inserts an implicit default value in the column. In any case, MySQL generates a warning instead of an error and continues to execute the statement. Section 13.1.5, "create table Syntax" describes implicit default values.

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Invalid date is not allowed in strict mode, for example, '2017-04-31 ′. It does not allow the date to use the "zero" part, for example, '2017-04-00' or "zero" date. To disable it, enable the no_zero_in_date and no_zero_date SQL modes based on the strict mode.

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If you do not use the strict mode (that is, do not enable strict_trans_tables or strict_all_tables mode), MySQL inserts the adjusted value and provides a warning for invalid or lost values. In strict mode, you can use insert ignore or update ignore. See section 13.5.4.22, "Show warnings Syntax ".

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The following special modes quickly combine the modes listed above.

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This includes all the mode values in most of the latest MySQL versions. In the old version, the combination mode does not include any unsuitable mode values in the new version.

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· ANSI

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It is equivalent to real_as_float, pipes_as_concat, ansi_quotes, and ignore_space. See section 1.8.3, "run MySql in ANSI mode ".

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· DB2

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Equivalent to pipes_as_concat, ansi_quotes, ignore_space, no_key_options, no_table_options, and no_field_options.

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· MaxDB

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Equivalent to pipes_as_concat, ansi_quotes, ignore_space, no_key_options, no_table_options, no_field_options, and no_auto_create_user.

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· MSSQL

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Equivalent to pipes_as_concat, ansi_quotes, ignore_space, no_key_options, no_table_options, and no_field_options.

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· Mysql323

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It is equivalent to no_field_options and high_not_precedence.

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· Mysql40

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It is equivalent to no_field_options and high_not_precedence.

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· Oracle

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Equivalent to pipes_as_concat, ansi_quotes, ignore_space, no_key_options, no_table_options, no_field_options, and no_auto_create_user.

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· PostgreSQL

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Equivalent to pipes_as_concat, ansi_quotes, ignore_space, no_key_options, no_table_options, and no_field_options.

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· Traditional

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Equivalent to strict_trans_tables, strict_all_tables, no_zero_in_date, no_zero_date, error_for_division_by_zero, no_auto_create_user