https://github.com/saylidholam/practice_sql
https://github.com/saylidholam/practice_sql
mysql-database
Last synced: about 2 months ago
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- Host: GitHub
- URL: https://github.com/saylidholam/practice_sql
- Owner: SayliDholam
- Created: 2024-02-11T08:49:51.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2024-08-19T18:40:34.000Z (10 months ago)
- Last Synced: 2025-03-27T12:12:43.252Z (3 months ago)
- Topics: mysql-database
- Homepage:
- Size: 132 KB
- Stars: 4
- Watchers: 1
- Forks: 0
- Open Issues: 0
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Metadata Files:
- Readme: README.md
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README
# Practice_SQL
Welcome to the Practice_SQL Repository!
This repository contains:
SQL query exercises covering various topics such as SELECT statements, JOIN operations, aggregrate functions, subqueries, and more.
### 1. Select Statements
The `SELECT` statement is used to retrieve data from a database. Here are some common variations:
- Basic SELECT: Retrieve all columns from a table.
```sql
SELECT * FROM table_name;
- SELECT with WHERE: Retrieve specific rows based on certain conditions.
```sql
SELECT column1, column2 FROM table_name WHERE condition;
- SELECT with ORDER BY: Retrieve data sorted in ascending or descending order.e.
```sql
SELECT column1, column2 FROM table_name ORDER BY column1 ASC;
### 2. Join Operations
JOIN operations are used to combine records from two or more tables. Common types include:
- INNER JOIN: Returns records that have matching values in both tables.
```sql
SELECT table1.column, table2.column
FROM table1
INNER JOIN table2 ON table1.common_column = table2.common_column;
- LEFT JOIN: Returns all records from the left table and matching records from the right table.
```sql
SELECT table1.column, table2.column
FROM table1
LEFT JOIN table2 ON table1.common_column = table2.common_column;
- RIGHT JOIN: Returns all records from the right table and matching records from the left table.
```sql
SELECT table1.column, table2.column
FROM table1
RIGHT JOIN table2 ON table1.common_column = table2.common_column;
### 3. Aggregate Functions
Aggregate functions perform calculations on a set of values and return a single value.
Common types include:
- COUNT(): Returns the number of rows that match a specified criterion.
```sql
SELECT COUNT(column_name) AS count_alias FROM table_name WHERE condition;
- SUM(): Returns the total sum of a numeric column.
```sql
SELECT SUM(column_name) AS sum_alias FROM table_name WHERE condition;
- AVG(): Returns the average value of a numeric column.
```sql
SELECT AVG(column_name) AS avg_alias FROM table_name WHERE condition;
- MAX(): Returns the maximum value from a column.
```sql
SELECT MAX(column_name) AS max_alias FROM table_name WHERE condition;
- MIN(): Returns the minimum value from a column.
```sql
SELECT MIN(column_name) AS min_alias FROM table_name WHERE condition;
### 4. Creating a Table
A Table is a combination of rows and columns.
For creating a table we have to define the structure of a table by adding names to columns and providing data type and size of data to be stored in columns.
- table_name: Specifies the name of the table to be created.
- column1, column2,: Defines the columns of the table.
- datatype: Specifies the data type for each column.
- constraints: Optional constraints such as PRIMARY KEY, FOREIGN KEY, NOT NULL, UNIQUE, etc., to enforce data integrity and rules on the columns.
```sql
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
...);
### 5. Inserting Records
The INSERT INTO statement is used to insert new records in a table.
- table_name: Specifies the name of the table where data will be inserted.
- column1, column2..: Specifies the columns to insert data into.
- VALUES: Keyword indicating the values to be inserted.
- value1, value2..: Actual values to be inserted into the respective columns.
```sql
INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...),
(value1, value2, ...)...;
### 6. Updating Records
The UPDATE statement in SQL is used to update the data of an existing table in the database.
We can update single columns as well as multiple columns using the UPDATE statement as per our requirement.
- table_name: Specifies the name of the table to update.
- column1, column2, ...: Specifies the columns to be updated.
- value1, value2, ...: Specifies the new values for the corresponding columns.
- condition: Specifies the condition to identify which rows to update.
```sql
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
### 7. Partitions:
Partitioning in SQL involves dividing large tables into smaller, more manageable parts.
It improves query performance, simplifies data management, and enhances data availability.
- table_name: Name of the table to be created.
- column1, column2, ...: Columns in the table.
- partitioning_method: Method used to partition the table (RANGE, LIST, HASH, KEY, etc.).
- partition_options: Options specific to the chosen partitioning method.
```sql
CREATE TABLE table_name (
column1 datatype,
column2 datatype,
...)
PARTITION BY partitioning_method (partition_options);
a. RANGE Partitioning:
- Partitions data based on ranges defined for a column.
```sql
PARTITION BY RANGE(column_name) (
PARTITION p1 VALUES LESS THAN (value1),
PARTITION p2 VALUES LESS THAN (value2),
...
PARTITION pN VALUES LESS THAN (valueN) );
b. LIST Partitioning:
- Partitions data based on a predefined list of values.
```sql
PARTITION BY LIST(column_name) (
PARTITION p1 VALUES IN (value1, value2, ...),
PARTITION p2 VALUES IN (value3, value4, ...),
...
PARTITION pN VALUES IN (valueN, valueN+1, ...));
c. HASH Partitioning:
- Distributes data uniformly across partitions using a hashing algorithm.
```sql
PARTITION BY HASH(column_name) PARTITIONS num_partitions;
d. KEY Partitioning:
- used for columns with unique values
```sql
PARTITION BY KEY(column_name) PARTITIONS num_partitions;