90 lines
2.2 KiB
Markdown
90 lines
2.2 KiB
Markdown
---
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title: SQL Union Operator
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---
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## SQL Union Operator
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### Description
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For this guide we'll discuss the UNION Operator section of the SQL statement.
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The UNION Operator is used to combine the results of multiple select statements into one result set.
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The SQL statements must have the same number of columns in their Select Statements, and the data types of those columns must also be equivalent.
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### Basic Example
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SQL Statement
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```sql
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SELECT 'aaaaa'
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UNION
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SELECT 'bbbbbbbbb';
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```
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Output
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```text
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+-----------+
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| aaaaa |
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+-----------+
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| aaaaa |
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| bbbbbbbbb |
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+-----------+
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2 rows in set (0.00 sec)
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```
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### Example using the student tables
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SQL Statement
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```sql
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SELECT StudentID, FullName FROM student WHERE studentID BETWEEN 1 AND 5
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UNION
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SELECT studentID, studentEmailAddr FROM `student-contact-info` WHERE studentID BETWEEN 7 AND 8;
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```
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Output
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``` text
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+-----------+--------------------------------+
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| StudentID | FullName |
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+-----------+--------------------------------+
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| 1 | Monique Davis |
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| 2 | Teri Gutierrez |
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| 3 | Spencer Pautier |
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| 4 | Louis Ramsey |
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| 5 | Alvin Greene |
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| 7 | Maximo.Smith@freeCodeCamp.org |
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| 8 | Michael.Roach@freeCodeCamp.ort |
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+-----------+--------------------------------+
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7 rows in set (0.00 sec)
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```
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## SQL UNION ALL Operator
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The UNION ALL operator is an extension of the UNION operator that results in A+B of rows in the ouptput assuming A and B are your inputs. The primary difference in UNION ALL is that it doesn't deduplicate rows from A+B. If a given input from A also exists in B, then both occurrences are returned.
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### Basic Syntax
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SQL Statement
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```sql
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SELECT expression1, expression2, ... expression_n
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FROM tables
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[WHERE conditions]
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UNION ALL
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SELECT expression1, expression2, ... expression_n
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FROM tables
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[WHERE conditions];
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```
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As with all of these SQL things there is MUCH MORE to them than what's in this introductory guide.
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I hope this at least gives you enough to get started.
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Please see the manual for your database manager and have fun trying different options yourself.
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