What is union clause and union all clause in MySQL?

The UNION command is used to combine more than one SELECT query results into a single query contain rows from all the select queries. … MySQL uses the DISTINCT clause as the default when executing UNION queries if nothing is specified. The ALL clause is used to return all even the duplicate rows in the UNION query.

What is Union and Union all in MySQL?

SQL Union Vs Union All Operator

Union Union All
It combines the result set from multiple tables with eliminating the duplicate records It combines the result set from multiple tables without eliminating the duplicate records
It performs a distinct on the result set. It does not perform distinct on the result set

What is the difference between Union and Union all clause in SQL?

UNION ALL command is equal to UNION command, except that UNION ALL selects all the values. The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all the rows from all the tables fitting your query specifics and combines them into a table.

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What is Union in MySQL?

The MySQL UNION operator is used to combine the result sets of 2 or more SELECT statements. It removes duplicate rows between the various SELECT statements. Each SELECT statement within the UNION operator must have the same number of fields in the result sets with similar data types.

What is the main difference between Union and Union all in DBMS?

The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all rows from all tables fitting your query specifics and combines them into a table. A UNION statement effectively does a SELECT DISTINCT on the results set.

Why UNION all is faster than UNION?

Because the UNION ALL operator does not remove duplicate rows, it runs faster than the UNION operator. The following are rules to union data: The number of columns in all queries must be the same.

How do you order by in UNION all?

Combining ORDER BY and UNION

  1. The columns in the ORDER BY list must be a subset of the columns in the select list of the left side of the union.
  2. All the columns in the ORDER BY list must be sorted in ascending order and they must be an in-order prefix of the columns in the target list of the left side of the UNION.

What is the use of union all?

The SQL UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It does not remove duplicate rows between the various SELECT statements (all rows are returned). Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types.

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What is difference between Union & Union all?

The only difference between Union and Union All is that Union extracts the rows that are being specified in the query while Union All extracts all the rows including the duplicates (repeated values) from both the queries.

Can union and union all return the same results?

UNION performs a deduplication step before returning the final results, UNION ALL retains all duplicates and returns the full, concatenated results. To allow success the number of columns, data types, and data order in each SELECT must be a match.

How do union queries work?

The Union operator combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the Union. In simple terms, it combines the two or more row sets and keeps duplicates. For example, the table ‘A’ has 1,2, and 3 and the table ‘B’ has 3,4,5.

What is the difference between union and inner join?

UNION vs.

The join such as INNER JOIN or LEFT JOIN combines columns from two tables while the UNION combines rows from two queries. In other words, join appends the result sets horizontally while union appends result set vertically.

What is a union join?

UNION. JOIN combines data from many tables based on a matched condition between them. SQL combines the result-set of two or more SELECT statements. It combines data into new columns. It combines data into new rows.

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