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- How to write grouping function in mysql
- The grouping function in MySQL is used to calculate aggregate values by grouping a data set. Commonly used functions are: SUM: Calculate the sum of the values in the specified column COUNT: Calculate the number of non-NULL values in the specified column AVG: Calculate the average value of the values in the specified column MIN: Calculate the minimum value in the specified column MAX: Calculate the number of non-NULL values in the specified column the maximum value of
- Mysql Tutorial . Database 1046 2024-04-29 04:30:23
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- What is the command to find table structure in mysql
- To find the structure of a MySQL table, you can use the DESCRIBE command followed by the name of the table you want to examine. The output will provide detailed information about each column in the table, including name, data type, nullability, key constraints, and default values.
- Mysql Tutorial . Database 724 2024-04-29 04:24:14
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- Usage of where in mysql
- The WHERE clause is used to filter MySQL data results and select rows that meet specific criteria by specifying conditions. Conditions can contain comparison operators, logical operators, wildcards, constants, and variables. Examples: - Filter based on age: SELECT FROM employees WHERE age > 18; - Filter based on name pattern: SELECT FROM customers WHERE name LIKE "John%"; - Filter based on multiple conditions: SELECT * FROM orders WHERE total_amount > 100 AND order_
- Mysql Tutorial . Database 504 2024-04-29 04:21:16
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- The role of unique index in mysql
- MySQL unique index ensures that each row in the database table has a unique specific column value, thereby: ensuring uniqueness and preventing duplicate values; providing fast search, using B-Tree data structure; maintaining data integrity and reducing redundant errors; optimization Improve space utilization and avoid duplicate value storage; improve query performance and quickly filter rows that meet unique index conditions.
- Mysql Tutorial . Database 956 2024-04-29 04:18:16
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- What is join in mysql
- JOIN in MySQL is a query command used to combine data from different tables by creating a temporary table by matching columns. There are four types of JOIN: INNER JOIN (matches only rows that exist in both tables), LEFT JOIN (selects all rows in the left table), RIGHT JOIN (selects all rows in the right table), and FULL JOIN (selects all rows in both tables). JOIN improves efficiency and readability by combining data, avoiding subqueries, simplifying queries, and more.
- Mysql Tutorial . Database 229 2024-04-29 04:15:26
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- How to use replace function in mysql
- The REPLACE() function in MySQL is used to replace characters or substrings in a string. Its syntax is: REPLACE(string, search_string, replace_string). It supports replacing multiple substrings simultaneously, using regular expressions for replacement, and replacing null values. For example, the following example replaces "Apple" with "Banana" in a string: SELECT REPLACE('I love Apple', 'Apple', 'Banana');
- Mysql Tutorial . Database 867 2024-04-29 04:09:15
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- How to write after on in inner join query in mysql
- The ON statement following the INNER JOIN is used to specify the columns used to compare and match the tables. The syntax is: ON = . Other points: 1. Operators can be replaced by >, = and
- Mysql Tutorial . Database 723 2024-04-29 04:06:16
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- The difference between inner join, left join and right join in mysql
- The difference between inner join, left join and right join in MySQL is that inner join only returns matching rows in both tables, while left join returns all rows of the left table, including matching right table rows, and right join returns all rows of the right table. , contains matching left table rows. Inner join syntax: SELECT * FROM table1 INNER JOIN table2 ON table1.column1 = table2.column2; Left join syntax: SELECT * FROM table1 LEFT JOIN table2 ON table1.column1 = table2.column2; Right join syntax: SELE
- Mysql Tutorial . Database 529 2024-04-29 04:00:36
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- Command to delete records in mysql
- The command to delete records in MySQL is DELETE. The syntax is: DELETE FROM table_name WHERE condition; where table_name is the target table and condition is the optional deletion condition. If no condition is specified, all records in the table are deleted.
- Mysql Tutorial . Database 340 2024-04-29 03:57:12
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- Command to delete columns in mysql
- The command to delete a column in MySQL is ALTER TABLE. The syntax is ALTER TABLE table_name DROP COLUMN column_name. It can be used to delete non-primary key columns. The data in the column before deletion must be empty or NULL. The data in the column will be lost after deletion. For InnoDB tables, The table will be rebuilt after deleting the column.
- Mysql Tutorial . Database 322 2024-04-29 03:54:13
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- The meaning of double expression in mysql
- The DOUBLE data type in MySQL is a 64-bit floating point number used to store high-precision floating point numbers. Features include: 1. Accuracy up to 15-16 significant digits; 2. Value range is -1.7976931348623157e+308 to 1.7976931348623157e+308; 3. Occupies 8 bytes of storage space. Suitable for scenarios that require high-precision floating point operations, such as scientific computing, financial modeling and statistical analysis.
- Mysql Tutorial . Database 196 2024-04-29 03:51:14
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- What is the round function in mysql?
- The ROUND function in MySQL is used to round numbers. The syntax is ROUND(number, decimal_places), where number is the number to be rounded, and decimal_places is the number of decimal places retained after rounding. For example, ROUND(123.456, 2) returns rounding The number to two decimal places is 123.46.
- Mysql Tutorial . Database 269 2024-04-29 03:48:14
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- Current date and time functions in mysql
- There are three functions in MySQL to obtain the current date and time: 1. NOW() function: returns the current date and time in the format of 'YYYY-MM-DD HH:MM:SS'; 2. CURDATE() function: returns the current Date, the format is 'YYYY-MM-DD'; 3. CURTIME() function: Returns the current time, the format is 'HH:MM:SS'.
- Mysql Tutorial . Database 532 2024-04-29 03:45:21
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- How to use like in mysql
- The LIKE operator is used for pattern matching in MySQL. It uses wildcards to match a sequence of characters, including: %: matches zero or more characters. _: Matches a single character. [ ]: Matches any characters listed within square brackets.
- Mysql Tutorial . Database 856 2024-04-29 03:42:14
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- The difference between describe and show in mysql
- DESCRIBE describes the table structure (column names, data types, constraints, indexes) and applies only to table objects. SHOW, on the other hand, displays metadata about database objects (databases, tables, columns, functions, procedures, and so on), including a brief list of columns in the table and runtime information about the database server.
- Mysql Tutorial . Database 466 2024-04-29 03:39:13
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