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196 lines
9.3 KiB
Markdown
196 lines
9.3 KiB
Markdown
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# Quick SQL Cheatsheet
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A quick reminder of all relevant SQL queries and examples on how to use them.
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This repository is constantly being updated and added to by the community.
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Pull requests are welcome. Enjoy!
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# Table of Contents
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1. [ Finding Data Queries. ](#find)
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2. [ Data Modification Queries. ](#modify)
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3. [ Reporting Queries. ](#report)
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4. [ Join Queries. ](#joins)
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5. [ View Queries. ](#view)
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6. [ Altering Table Queries.](#alter)
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7. [ Creating Table Query.](#create)
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<a name="find"></a>
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# 1. Finding Data Queries
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### **SELECT**: used to select data from a database
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* `SELECT` * `FROM` table_name;
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### **DISTINCT**: filters away duplicate values and returns rows of specified column
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* `SELECT DISTINCT` column_name;
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### **WHERE**: used to filter records/rows
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* `SELECT` column1, column2 `FROM` table_name `WHERE` condition;
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* `SELECT` * `FROM` table_name `WHERE` condition1 `AND` condition2;
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* `SELECT` * `FROM` table_name `WHERE` condition1 `OR` condition2;
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* `SELECT` * `FROM` table_name `WHERE NOT` condition;
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* `SELECT` * `FROM` table_name `WHERE` condition1 `AND` (condition2 `OR` condition3);
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* `SELECT` * `FROM` table_name `WHERE EXISTS` (`SELECT` column_name `FROM` table_name `WHERE` condition);
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### **ORDER BY**: used to sort the result-set in ascending or descending order
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* `SELECT` * `FROM` table_name `ORDER BY` column;
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* `SELECT` * `FROM` table_name `ORDER BY` column `DESC`;
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* `SELECT` * `FROM` table_name `ORDER BY` column1 `ASC`, column2 `DESC`;
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### **SELECT TOP**: used to specify the number of records to return from top of table
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* `SELECT TOP` number columns_names `FROM` table_name `WHERE` condition;
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* `SELECT TOP` percent columns_names `FROM` table_name `WHERE` condition;
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* Not all database systems support `SELECT TOP`. The MySQL equivalent is the `LIMIT` clause
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* `SELECT` column_names `FROM` table_name `LIMIT` offset, count;
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### **LIKE**: operator used in a WHERE clause to search for a specific pattern in a column
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* % (percent sign) is a wildcard character that represents zero, one, or multiple characters
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* _ (underscore) is a wildcard character that represents a single character
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* `SELECT` column_names `FROM` table_name `WHERE` column_name `LIKE` pattern;
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* `LIKE` ‘a%’ (find any values that start with “a”)
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* `LIKE` ‘%a’ (find any values that end with “a”)
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* `LIKE` ‘%or%’ (find any values that have “or” in any position)
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* `LIKE` ‘_r%’ (find any values that have “r” in the second position)
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* `LIKE` ‘a_%_%’ (find any values that start with “a” and are at least 3 characters in length)
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* `LIKE` ‘[a-c]%’ (find any values starting with “a”, “b”, or “c”
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### **IN**: operator that allows you to specify multiple values in a WHERE clause
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* essentially the IN operator is shorthand for multiple OR conditions
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* `SELECT` column_names `FROM` table_name `WHERE` column_name `IN` (value1, value2, …);
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* `SELECT` column_names `FROM` table_name `WHERE` column_name `IN` (`SELECT STATEMENT`);
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### **BETWEEN**: operator selects values within a given range inclusive
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* `SELECT` column_names `FROM` table_name `WHERE` column_name `BETWEEN` value1 `AND` value2;
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* `SELECT` * `FROM` Products `WHERE` (column_name `BETWEEN` value1 `AND` value2) `AND NOT` column_name2 `IN` (value3, value4);
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* `SELECT` * `FROM` Products `WHERE` column_name `BETWEEN` #01/07/1999# AND #03/12/1999#;
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### **NULL**: values in a field with no value
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* `SELECT` * `FROM` table_name `WHERE` column_name `IS NULL`;
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* `SELECT` * `FROM` table_name `WHERE` column_name `IS NOT NULL`;
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### **AS**: aliases are used to assign a temporary name to a table or column
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* `SELECT` column_name `AS` alias_name `FROM` table_name;
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* `SELECT` column_name `FROM` table_name `AS` alias_name;
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* `SELECT` column_name `AS` alias_name1, column_name2 `AS` alias_name2;
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* `SELECT` column_name1, column_name2 + ‘, ‘ + column_name3 `AS` alias_name;
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### **UNION**: set operator used to combine the result-set of two or more SELECT statements
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* Each SELECT statement within UNION must have the same number of columns
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* The columns must have similar data types
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* The columns in each SELECT statement must also be in the same order
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* `SELECT` columns_names `FROM` table1 `UNION SELECT` column_name `FROM` table2;
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* `UNION` operator only selects distinct values, `UNION ALL` will allow duplicates
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### **INTERSECT**: set operator which is used to return the records that two SELECT statements have in common
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* Generally used the same way as **UNION** above
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* `SELECT` columns_names `FROM` table1 `INTERSECT SELECT` column_name `FROM` table2;
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### **EXCEPT**: set operator used to return all the records in the first SELECT statement that are not found in the second SELECT statement
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* Generally used the same way as **UNION** above
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* `SELECT` columns_names `FROM` table1 `EXCEPT SELECT` column_name `FROM` table2;
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### **ANY|ALL**: operator used to check subquery conditions used within a WHERE or HAVING clauses
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* The `ANY` operator returns true if any subquery values meet the condition
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* The `ALL` operator returns true if all subquery values meet the condition
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* `SELECT` columns_names `FROM` table1 `WHERE` column_name operator (`ANY`|`ALL`) (`SELECT` column_name `FROM` table_name `WHERE` condition);
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### **GROUP BY**: statement often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns
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* `SELECT` column_name1, COUNT(column_name2) `FROM` table_name `WHERE` condition `GROUP BY` column_name1 `ORDER BY` COUNT(column_name2) DESC;
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### **HAVING**: this clause was added to SQL because the WHERE keyword could not be used with aggregate functions
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* `SELECT` `COUNT`(column_name1), column_name2 `FROM` table `GROUP BY` column_name2 `HAVING` `COUNT(`column_name1`)` > 5;
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### **WITH**: often used for retrieving hierarchical data or re-using temp result set several times in a query. Also referred to as "Common Table Expression"
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* `WITH RECURSIVE` cte `AS` (<br/>
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`SELECT` c0.* `FROM` categories `AS` c0 `WHERE` id = 1 `# Starting point`<br/>
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`UNION ALL`<br/>
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`SELECT` c1.* `FROM` categories `AS` c1 `JOIN` cte `ON` c1.parent_category_id = cte.id<br/>
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)<br/>
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`SELECT` *<br/>
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`FROM` cte
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<a name="modify"></a>
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# 2. Data Modification Queries
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### **INSERT INTO**: used to insert new records/rows in a table
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* `INSERT INTO` table_name (column1, column2) `VALUES` (value1, value2);
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* `INSERT INTO` table_name `VALUES` (value1, value2 …);
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### **UPDATE**: used to modify the existing records in a table
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* `UPDATE` table_name `SET` column1 = value1, column2 = value2 `WHERE` condition;
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* `UPDATE` table_name `SET` column_name = value;
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### **DELETE**: used to delete existing records/rows in a table
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* `DELETE FROM` table_name `WHERE` condition;
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* `DELETE` * `FROM` table_name;
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<a name="report"></a>
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# 3. Reporting Queries
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### **COUNT**: returns the # of occurrences
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* `SELECT COUNT (DISTINCT` column_name`)`;
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### **MIN() and MAX()**: returns the smallest/largest value of the selected column
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* `SELECT MIN (`column_names`) FROM` table_name `WHERE` condition;
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* `SELECT MAX (`column_names`) FROM` table_name `WHERE` condition;
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### **AVG()**: returns the average value of a numeric column
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* `SELECT AVG (`column_name`) FROM` table_name `WHERE` condition;
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### **SUM()**: returns the total sum of a numeric column
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* `SELECT SUM (`column_name`) FROM` table_name `WHERE` condition;
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<a name="joins"></a>
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# 4. Join Queries
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### **INNER JOIN**: returns records that have matching value in both tables
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* `SELECT` column_names `FROM` table1 `INNER JOIN` table2 `ON` table1.column_name=table2.column_name;
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* `SELECT` table1.column_name1, table2.column_name2, table3.column_name3 `FROM` ((table1 `INNER JOIN` table2 `ON` relationship) `INNER JOIN` table3 `ON` relationship);
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### **LEFT (OUTER) JOIN**: returns all records from the left table (table1), and the matched records from the right table (table2)
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* `SELECT` column_names `FROM` table1 `LEFT JOIN` table2 `ON` table1.column_name=table2.column_name;
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### **RIGHT (OUTER) JOIN**: returns all records from the right table (table2), and the matched records from the left table (table1)
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* `SELECT` column_names `FROM` table1 `RIGHT JOIN` table2 `ON` table1.column_name=table2.column_name;
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### **FULL (OUTER) JOIN**: returns all records when there is a match in either left or right table
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* `SELECT` column_names `FROM` table1 ``FULL OUTER JOIN`` table2 `ON` table1.column_name=table2.column_name;
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### **Self JOIN**: a regular join, but the table is joined with itself
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* `SELECT` column_names `FROM` table1 T1, table1 T2 `WHERE` condition;
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<a name="view"></a>
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# 5. View Queries
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### **CREATE**: create a view
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* `CREATE VIEW` view_name `AS SELECT` column1, column2 `FROM` table_name `WHERE` condition;
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### **SELECT**: retrieve a view
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* `SELECT` * `FROM` view_name;
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### **DROP**: drop a view
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* `DROP VIEW` view_name;
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<a name="alter"></a>
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# 6. Altering Table Queries
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### **ADD**: add a column
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* `ALTER TABLE` table_name `ADD` column_name column_definition;
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### **MODIFY**: change data type of column
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* `ALTER TABLE` table_name `MODIFY` column_name column_type;
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### **DROP**: delete a column
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* `ALTER TABLE` table_name `DROP COLUMN` column_name;
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<a name="create"></a>
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# 7. Creating Table Query
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### **CREATE**: create a table
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* `CREATE TABLE` table_name `(` <br />
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`column1` `datatype`, <br />
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`column2` `datatype`, <br />
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`column3` `datatype`, <br />
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`column4` `datatype`, <br />
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`);`
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