Article Introduction：The difference between UNION and UNION ALL in MySQL is that UNION eliminates duplicate rows, while UNION ALL retains all rows. UNION sorts the result set implicitly, but UNION ALL does not.

2024-04-27comment 0466

Article Introduction：In MySQL, UNION and UNION ALL are used to merge result sets. The difference lies in the way duplicate rows are handled. UNION removes duplicate rows, while UNION ALL retains all rows. UNION syntax: SELECT column 1, column 2, ...FROM table 1 UNION SELECT column 1, column 2, ...FROM table 2; UNION ALL syntax: SELECT column 1, column 2, ...FROM table 1 UNION ALL SELECT column 1, column 2, ...FROM table 2;

2024-04-27comment 0888

Article Introduction：Difference between UNION and UNION ALL set operators in MySQL: UNION returns unique rows, while UNION ALL returns all rows, including duplicate rows. UNION sorts the result set in ascending order, while UNION ALL does not sort. Select UNION to eliminate duplicate rows, and UNION ALL to retain duplicate rows.

2024-04-26comment 0313

Article Introduction：The difference between UNION and UNION ALL in Oracle is the way duplicate rows are handled. UNION removes duplicate rows and returns only distinct rows; UNION ALL retains all rows, including duplicates.

2024-04-30comment717

Article Introduction：UNION only returns unique rows, while UNION ALL contains duplicate rows; UNION deduplicates rows before merging, but UNION ALL does not deduplicate rows.

2024-05-02comment 0492

Article Introduction：If we need to combine the query results of the two tables and display them, we can use union and union all. Union all is to directly merge the result sets together, and union is to filter the merged result set, remove duplicate results, and then output it.

2020-06-12comment 03629

Article Introduction：1. Usage of union and unionall in SQL If we need to display the results of two select statements as a whole, we need to use the union or unionall keyword. The function of union (or union) is to combine multiple results and display them together. The difference between union and unionall is that union will automatically compress duplicate results in multiple result sets, while unionall will display all results, regardless of whether they are duplicates. union: performs a union operation on two result sets, excluding duplicate rows, and performs sorting by default rules; union will filter out duplicate records after table linking, so in table linking

2023-05-26comment 01250

Article Introduction：Union is a SQL operator used to combine the results of multiple SELECT statements into a result set. Its syntax is "UNION ALL SELECT * FROM TableB UNION SELECT * FROM TableC".

2020-06-09comment 08565

Article Introduction：UNION ALL is used in Oracle to merge result sets from different tables or subqueries while retaining duplicate rows. The specific usage is as follows: merge rows in different tables: SELECT FROM table 1 UNION ALL SELECT FROM table 2 merge duplicate rows in the same table: SELECT FROM table UNION ALL SELECT FROM table

2024-04-30comment320

Article Introduction：The UNION operation combines rows from different tables into a single result set, removing duplicate rows. The syntax format is: SELECT column_list FROM table1 UNION SELECT column_list FROM table2..., where table1 and table2 are the tables to be merged. The UNION operation requires that the participating tables have the same number of columns and data types, and that duplicate rows are removed.

2024-05-02comment 0732

Article Introduction：UNION ALL 是 SQL 中合并 SELECT 查询结果的运算符，特点是不去除重复行，用于合并具有相同列和数据类型的查询结果，例如合并不同表的数据、附加行到结果集等，与 UNION 运算符的区别在于 UNION 会去除重复行。

2024-05-24comment938

Article Introduction：The difference between UNION and JOIN in SQL: UNION merges rows of tables with the same structure and eliminates duplicates; JOIN joins rows of tables based on conditions, allowing different structures. UNION performance is generally faster than JOIN, but requires the same structural table; JOIN is flexible but may have lower performance.

2024-05-02comment 0476

Article Introduction：The usage of UNION in Oracle is to merge multiple query result sets with the same structure into a single result set. This operator removes duplicate records unless UNION ALL is used, which merges all records, including duplicates.

2024-04-30comment604

Article Introduction："Union all" means "join all", which means to perform a union operation on two result sets, including duplicate rows, without sorting. The UNION operator is used to merge the result sets of two or more SELECT statements; the SELECT statements inside UNION need to have the same number of columns, and the columns need to have similar data types.

2020-06-28comment 062029

Article Introduction：The UNION operator is used in SQL to merge rows with the same structure, producing a table containing all unique rows. It works by merging result sets, removing duplicate rows and returning remaining rows. Unlike UNION ALL, UNION returns only unique rows. When using UNION, note that both tables must have the same number of columns and data types.

2024-04-29comment273

Article Introduction：MySQL 的 UNION 操作符用于组合不同表或相同表中多个结果集，返回一个包含唯一行的组合结果。它需要确保列数和数据类型相同，使用 UNION ALL 时重复行将被保留，否则将被移除。

2024-06-12comment601

Article Introduction：In MySQL, the UNION operator merges result sets from multiple tables or subqueries, returning only unique result rows. It is primarily used to merge disjoint result sets and allows retaining duplicate rows via UNION ALL.

2024-04-26comment 0158

Article Introduction：In mysql, the usage of union all is "select statement 1 union all select statement 2...". Union all can combine the results from multiple select statements into a result set and return all records. Such efficiency Will be higher than union.

2022-05-07comment 04184

Article Introduction：The use of union in C language is a special data type that allows different data types to be stored in the same memory location. The use of union can help us save memory space and facilitate conversion between different data types. When using union, you need to note that the corresponding member is valid and only one member can be accessed at the same time.

2023-09-27comment 0682

Article Introduction：In Oracle, union is used to combine the results of two SQL statements and exclude duplicate data. The field types of the two select statements match, and the number of fields must be the same. The syntax is "select column,... from table1 union select column,...from table2".

2022-06-17comment 04049