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- Can from be followed by case in mysql?
- Yes, MySQL allows the use of CASE expressions in the FROM clause to select specific rows, the syntax is: SELECT ... FROM table_name WHERE AND CASE WHEN THEN WHEN THEN ELSE END AS where
- Mysql Tutorial . Database 960 2024-05-01 20:57:41
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- What does whwre mean in mysql?
- The WHERE clause is used to specify filter conditions in MySQL queries to filter matching records from the result set. Its syntax structure is: SELECT * FROM table_name WHERE condition;. The WHERE clause can be used to display only records that meet certain criteria, exclude unnecessary records, and group or sort query results. A condition consists of an operator and an operand, which can be a column name, a constant, or an expression. Operators include "=", "!=", ">", "=", and "
- Mysql Tutorial . Database 952 2024-05-01 20:57:17
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- How to correct field errors in mysql
- "Unknown column" errors with the FIELD() function in MySQL are usually caused by misspelling of the column name, non-existence of the column, or insufficient permissions. Fix: Check the spelling of the column name in the FIELD() function. Use the SHOW COLUMNS query to confirm whether the column exists. Use a SELECT query to check access to a column. If the above steps cannot solve the problem, it is recommended to back up the data and try to repair the table or database.
- Mysql Tutorial . Database 781 2024-05-01 20:54:39
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- How to calculate the length of enum in mysql
- The length of the ENUM data type in MySQL depends on the number of characters stored and the number of bytes in the character set. The calculation formula is: number of characters stored × number of bytes in the character set.
- Mysql Tutorial . Database 940 2024-05-01 20:54:15
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- What does or mean in mysql
- In MySQL, the OR operator (||) joins multiple conditions and returns true as long as one of the conditions is true. It is used to find data that meets multiple criteria, combine subquery results, and create complex search criteria.
- Mysql Tutorial . Database 467 2024-05-01 20:51:50
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- What does as mean in mysql
- ASAS in MySQL is a keyword used to create an alias or specify a new table name. It improves readability, avoids ambiguity, performs temporary renaming, and creates table aliases. Aliases created using AS are only valid within the current query by default, but permanent aliases can be created using the CREATE ALIAS statement.
- Mysql Tutorial . Database 956 2024-05-01 20:49:01
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- What does acid in mysql mean?
- ACID in MySQL includes atomicity, consistency, isolation, and durability. Atomicity ensures that all transactions succeed or fail; consistency ensures that the database state remains consistent before and after the transaction; isolation ensures that concurrent transactions do not affect each other; and durability ensures that submitted modifications are permanently saved.
- Mysql Tutorial . Database 405 2024-05-01 20:48:39
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- What does analyze in mysql do?
- The MySQL ANALYZE command updates table statistics to optimize query performance, including statistics updates, query optimizer improvements, and space release. It works by scanning table data to calculate the number of rows, the number of DISTINCT values, and the distribution of values to generate a more optimized query plan. Perform ANALYZE on frequently queried tables regularly and analyze only key columns for best practices.
- Mysql Tutorial . Database 792 2024-05-01 20:48:14
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- How to use orderby in mysql
- MySQL's ORDER BY clause is used to sort query results by a specified column. It supports ascending (ASC) and descending (DESC) sorting and can sort multiple columns simultaneously. NULL values are usually treated as the smallest value, but they can be treated as the largest value using the COALESCE() function. The ORDER BY clause also allows sorting using expressions and can optimize sort performance by creating indexes, using covering indexes, and limiting the number of rows returned.
- Mysql Tutorial . Database 398 2024-05-01 20:46:05
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- How to view all tables in the database in mysql
- To view all tables in a MySQL database, you can use the SHOW TABLES; command, which displays a list of all tables, including table name, type, and row count (if INFORMATION_SCHEMA is enabled).
- Mysql Tutorial . Database 677 2024-05-01 20:45:43
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- How many Chinese characters can be stored in varchar(50) in mysql
- The VARCHAR(50) type in MySQL can store up to 25 Chinese characters, which is affected by the character encoding. For example, 16 Chinese characters can be stored using UTF-8 encoding, and 25 Chinese characters can be stored using GBK encoding. It should be noted that the actual storage space will vary according to the data length, and excess characters will be truncated when the limit is exceeded.
- Mysql Tutorial . Database 821 2024-05-01 20:45:23
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- The relationship between where and having in mysql
- The WHERE clause filters row-level data, while the HAVING clause filters group-level data. The WHERE clause is applied after the FROM keyword, while the HAVING clause is applied after the GROUP BY keyword.
- Mysql Tutorial . Database 654 2024-05-01 20:42:35
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- where and what cannot be used together in mysql
- The WHERE clause cannot be used with the ORDER BY, GROUP BY, and HAVING clauses. These clauses must be applied in order: first WHERE, then GROUP BY, then HAVING, and finally ORDER BY.
- Mysql Tutorial . Database 375 2024-05-01 20:42:13
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- The difference between where and on in mysql
- The difference between WHERE and ON in MySQL is: Usage: WHERE is used to filter records, while ON is used to join tables. Statements: WHERE is used in SELECT, UPDATE, DELETE statements, while ON is used in JOIN statements. Clause: WHERE condition is in WHERE clause and ON condition is in ON clause. Scope: WHERE can only be used for a single table, while ON can be used to join multiple tables. Purpose: WHERE is used to filter data, while ON is used to establish relationships between tables.
- Mysql Tutorial . Database 940 2024-05-01 20:40:02
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- The difference between varchar and nvarchar in mysql
- The main difference between VarChar and NVarChar is the supported character set: VarChar only supports ASCII or Latin1 character set, while NVarChar supports Unicode character set, which means that NVarChar can store a wider variety of characters, including Chinese characters, Japanese characters, etc.
- Mysql Tutorial . Database 560 2024-05-01 20:39:40
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