Awesome-SQL

These 75+ queries will help to learn sql.

Oracle
MySQL
SQL Server
PostgreSQL
SQLite

Table

Create a Table with a few fields by specifying their data types.

  CREATE TABLE user (
    user_id INT PRIMARY KEY,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    email VARCHAR(255) UNIQUE,
    password VARCHAR(255),
    date_created DATETIME
  );

Add a field to an existing table.

  ALTER TABLE user ADD gender VARCHAR(25);

Modify a field's data type of a table.

  ALTER TABLE user MODIFY COLUMN date_created VARCHAR(255);

Rename a field's name.

  ALTER TABLE user RENAME COLUMN email TO email_id;

Remove a field from a table.

  ALTER TABLE user DROP COLUMN gender;

Rename a table's name.

  ALTER TABLE user RENAME TO user_detail;

Drop a table.

  DROP TABLE user_detail;

Constraints

Primary Key

Create a Table with
- a single field as the primary key
- 2 or, more fields as the primary key

  CREATE TABLE one_primary_key (user_id INT PRIMARY KEY,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
  );
  
  CREATE TABLE two_primary_keys (id int,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    CONSTRAINT PK_primary_keys PRIMARY KEY (id, first_name)
  );

Add a primary key to an existing table
- for a single field
- for 2 or, more fields

  CREATE TABLE no_primary_key (id INT,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
  );
  
  ALTER TABLE no_primary_key ADD PRIMARY KEY (id);

  ALTER TABLE no_primary_key ADD CONSTRAINT PK_primary_keys PRIMARY KEY (id, first_name);

Unique

Create a Table with
- a single field unique
- 2 or, more fields combining unique
- multiple unique fields

  CREATE TABLE one_unique (
    id INT,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    email VARCHAR(255) UNIQUE
  );

  CREATE TABLE two_unique (id int,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    CONSTRAINT UQ_two_unique UNIQUE (first_name, last_name)
  );

Add a unique constraint to an existing table
- for a single field
- for 2 or, more fields combining
Drop a unique constraint

  CREATE TABLE no_unique (id INT,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
  );

  ALTER TABLE no_unique ADD UNIQUE (id);
  ALTER TABLE no_unique DROP INDEX id;

  ALTER TABLE no_unique ADD CONSTRAINT UQ_no_unique UNIQUE (id, first_name);
  ALTER TABLE no_unique DROP INDEX UQ_no_unique;

Not Null

Create a Table with
- one NOT NULL field
- multiple NOT NULL fields
- Add NOT NULL constraint to an existing field
- Remove NOT NULL constraint from an existing field

  CREATE TABLE one_not_null (id INT NOT NULL,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
  );

  CREATE TABLE two_not_null (id INT NOT NULL,
    first_name VARCHAR(255) NOT NULL,
    last_name VARCHAR(255)
  );

  ALTER TABLE one_not_null MODIFY COLUMN first_name VARCHAR(255) NOT NULL;
  ALTER TABLE two_not_null MODIFY COLUMN first_name VARCHAR(255);

Default

Create a Table with DEFAULT value(s)
- for one field
- multiple fields
- Add a DEFAULT value constraint to an existing field
- Remove DEFAULT value constraint from an existing field

  CREATE TABLE one_default (id INT NOT NULL,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    gender VARCHAR(255) DEFAULT 'unknown'
  );

  CREATE TABLE two_default (id INT NOT NULL,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    gender VARCHAR(255) DEFAULT 'unknown',
    bio VARCHAR(255) DEFAULT '...'
  );

  ALTER TABLE one_default ALTER first_name SET DEFAULT 'Goodie';
  ALTER TABLE one_default ALTER first_name DROP DEFAULT;

Check

Create a Table with CHECK constraint for

a single field
2 or, more fields combining
multiple separated fields

CREATE TABLE one_check (id INT NOT NULL,
  first_name VARCHAR(255),
  last_name VARCHAR(255),
  age int CHECK (age>=18)
);

CREATE TABLE combined_check (id INT NOT NULL,
  first_name VARCHAR(255),
  last_name VARCHAR(255),
  age int, 
  cgpa DOUBLE,
  CONSTRAINT CHK_combined_check CHECK (age>=18 and cgpa>=7.5)
);

CREATE TABLE two_check (id INT NOT NULL,
  first_name VARCHAR(255),
  last_name VARCHAR(255),
  age int CHECK (age>=18),
  cgpa DOUBLE CHECK (cgpa>=7.5)
);

Add a CHECK constraint to an existing table

a single field
2 or, more fields combining

CREATE TABLE one_check (id INT NOT NULL,
  first_name VARCHAR(255),
  last_name VARCHAR(255),
  age int,
  cgpa DOUBLE
);

ALTER TABLE one_check ADD CHECK (age>=18);
ALTER TABLE one_check ADD CONSTRAINT CHK_one_check CHECK (age>=18 AND cgpa>=7.5);

Drop a CHECK constraint

SHOW CREATE TABLE one_check;
+ -----------
CREATE TABLE `one_check` (
  `id` int NOT NULL,
  `first_name` varchar(255) DEFAULT NULL,
  `last_name` varchar(255) DEFAULT NULL,
  `age` int DEFAULT NULL,
  CONSTRAINT `one_check_chk_1` CHECK ((`age` >= 18))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+ -----------

`user the conatra`
ALTER TABLE one_check DROP CHECK one_check_chk_1;

Foreign Key

Create a Table with

a single foreign key field

CREATE TABLE Persons (
  ID int NOT NULL,
  LastName varchar(255) NOT NULL,
  FirstName varchar(255),
  Age int,
  PRIMARY KEY (ID)
);

CREATE TABLE Orders (
  OrderID int NOT NULL,
  OrderNumber int NOT NULL,
  PersonID int,
  PRIMARY KEY (OrderID),
  FOREIGN KEY (PersonID) REFERENCES Persons(ID)
);

multiple foreign key fields

CREATE TABLE Persons (
  ID int NOT NULL,
  LastName varchar(255) NOT NULL,
  FirstName varchar(255),
  Age int,
  PRIMARY KEY (ID)
);

CREATE TABLE Address (
  AddressID int NOT NULL,
  Address_1 varchar(255) NOT NULL,
  Address_2 varchar(255),
  city varchar(255),
  country varchar(255),
  pincode varchar(255),
  PRIMARY KEY (AddressID)
);

CREATE TABLE Orders (
  OrderID int NOT NULL,
  OrderNumber int NOT NULL,
  PersonID int,
  AddressID int,
  PRIMARY KEY (OrderID),
  FOREIGN KEY (PersonID) REFERENCES Persons(ID),
  FOREIGN KEY (AddressID) REFERENCES Address(AddressID)
);

Add a foreign key constraint to existing table

a single field

CREATE TABLE Persons (
  ID int NOT NULL,
  LastName varchar(255) NOT NULL,
  FirstName varchar(255),
  Age int,
  PRIMARY KEY (ID)
);

CREATE TABLE Orders (
    OrderID int NOT NULL,
    OrderNumber int NOT NULL,
    PersonID int,
    PRIMARY KEY (OrderID)
);

ALTER TABLE Orders ADD FOREIGN KEY (PersonID) REFERENCES Persons(ID);

Drop a foreign key

ALTER TABLE Orders DROP CONSTRAINT orders_ibfk_1;

Insert, Update, Delete
- Insert a row into a table.
- Insert a row into a table by providing data for a few fields.
- Insert multiple rows at a time into a table.
- Insert into a table by selecting needed data from another table.
- Update a specific field's data in a table.
- Update a field's data for multiple rows at a time.
- Delete a row from a table.
- Delete multiple rows from a table.
Select
- Fetch all rows from a table.
- Fetch only specific fields' data from a table.
- Fetch only those rows that match a condition.
- Apply multiple conditions.
- Check if a field's data is NULL.
- Check if a field's data is not NULL.
- Check if a field's data starts with "NewY"
- Check if a field's data ends with "don"
- Check if a field's data contains "ijin"
- Check if a field's data has "a" at 2nd position
- Check if a field's data starts with "B" and, has at least 5 characters.
- Check if a field's data starts with "B" and, ends with "a".
- Check if a field's data starts with "a" or, "o".
- Check if a field's data doesn't contain "a" or, "o" at the 2nd position.
- Check if a field's data ends with any character from "m" to "t".
- Check if a field's data is 1 or, 2 or, 3 or, 4 or, 5.
- Check if a field's data is in the range of 10 to 30.
- Check if a field's data is not in the range of 10 to 50.
- Fetch only distinct data contained in a field.
- Fetch only the first 10 rows.
- Fetch rows from 21 to 40.
- Find the minimum value of a field.
- Find the maximum value of a field.
- Find the average value of a field.
- Find the sum of all values contained in a field.

References

(Swapna Kumar) - https://twitter.com/swapnakpanda/status/1554435629886218240
(W3 Schools) - https://www.w3schools.com/sql/

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