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Matthew Huntington 2 years ago
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SQL/lessons/sql_1.md
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@ -12,7 +12,7 @@
## Connect to Postgres through CLI ## Connect to Postgres through CLI
Since we used homebrew to install, use this command to start up the postgres enviornment (this is like running mongod when we were using MongoDB). If you used homebrew to install, use this command to start up the postgres enviornment.
``` ```
brew services start postgresql brew services start postgresql
@ -40,13 +40,24 @@ Once inside the `psql` app, you can list the sub databases like this:
## Create a Database ## Create a Database
Like MongoDB, Postgres has "sub-databases": Postgres has "sub-databases" (probably one for each app that you build)
Create a new database
```SQL ```SQL
CREATE DATABASE foo; -- create the sub database foo CREATE DATABASE foo;
DROP DATABASE foo; -- drop it ```
CREATE DATABASE test_db;
\connect test_db; -- connect to the test_db sub database Delete (drop) a database:
```sql
DROP DATABASE foo;
```
Connect to a different database:
```sql
\connect test_db;
``` ```
## Data types ## Data types
@ -62,50 +73,151 @@ Postgres has the following data types:
## Create a table ## Create a table
- Instead of collections, we have tables, which are just like a spreadsheet, or grid. Rows are entries, and columns are properties of each row. - Inside a database, we have tables, which are just like a spreadsheet or grid. Rows are entries, and columns are properties of each row.
- Unlike MongoDB, you have to tell Postgres, what data type each column is. It's very 'strict' - You have to tell Postgres what data type each column is. It's very 'strict'
Create a table called 'foo' with one column called 'name' which is a small text column:
```sql
CREATE TABLE foo ( name varchar(20) );
```
List (describe) your tables:
```sql
\dt
```
Delete (drop) a table:
```sql
DROP TABLE foo;
```
Create table with multiple columns
- `id` is a `serial`, which is a special integer that increments each time a new row is created)
- `name` is a 20 character string
- `age` is an integer
- `email` is a 32 character string
```sql
CREATE TABLE users ( id serial, name varchar(20), age int, email varchar(32) ); -
```
Describe the columns of the `users` table
```sql ```sql
CREATE TABLE foo ( name varchar(20) ); -- create a table called 'foo' with one column called 'name' which is a small text column \d users;
\dt -- describe your tables
DROP TABLE foo; -- drop a table
CREATE TABLE users ( id serial, name varchar(20), age int, email varchar(32) ); -- 'test' table has an id column, which is just a number, and a name column
\d users; -- describe the columns of the test sub database
``` ```
## Insert into the table ## Insert into the table
Make sure your values are in the same order that you specify they will be. You can move them around as you like, as long as you're consistent
```sql ```sql
INSERT INTO users ( name, age, email ) VALUES ( 'Matt', 36, 'matt.huntington@generalassemb.ly'); -- create a row INSERT INTO users ( name, age, email ) VALUES ( 'Matt', 36, 'matt.huntington@generalassemb.ly');
``` ```
## Select from table ## Select from table
There are lots of ways to alter how you retrieve data from a table:
Select all rows from the users table. Display only the name column
```sql ```sql
SELECT name FROM users; -- select all rows from the users table. display only the name column SELECT name FROM users;
SELECT * FROM users; -- select all rows from the users table. display only the all columns ```
SELECT * FROM users WHERE name = 'Matt'; -- select all rows from the user table where the name column is set to 'Matt'
SELECT * FROM users WHERE name LIKE '%Matt%'; -- select all rows from the user table where the name column contains 'Matt' Select all rows from the users table. Display all columns
SELECT * FROM users WHERE name = 'Matt' AND email = 'matt.huntington@generalassemb.ly'; -- select all rows from the user table where the name column is set to 'Matt' AND the email column is set to matt.huntington@generalassemb.ly
SELECT * FROM users WHERE name = 'Matt' OR email = 'matt.huntington@generalassemb.ly'; -- select all rows from the user table where either the name column is set to 'Matt' OR the email column is set to matt.huntington@generalassemb.ly ```sql
SELECT * FROM users WHERE age = 36; -- select all rows from the user table where the age column is set to 36 SELECT * FROM users;
SELECT * FROM users WHERE age != 16; -- select all rows from the user table where the age column is not set to 16 ```
SELECT * FROM users WHERE age > 26; -- select all rows from the user table where the age column is greater than 26
SELECT * FROM users WHERE age < 46; -- select all rows from the user table where the age column is less than 26 Select all rows from the user table where the name column is set to 'Matt'
SELECT * FROM users WHERE age <= 36; -- select all rows from the user table where the age column is less than or equal to 36
SELECT * FROM users WHERE age >= 36; -- select all rows from the user table where the age column is greater than or equal to 36 ```sql
SELECT * FROM users WHERE age IS NULL; -- select all rows from the user table where the age column has no value SELECT * FROM users WHERE name = 'Matt';
SELECT * FROM users WHERE age IS NOT NULL; -- select all rows from the user table where the age column has any value ```
Select all rows from the user table where the name column *contains* 'Matt' as a substring
```sql
SELECT * FROM users WHERE name LIKE '%Matt%';
```
Select all rows from the user table where the name column is set to 'Matt' AND the email column is set to matt.huntington@gmail.com
```sql
SELECT * FROM users WHERE name = 'Matt' AND email = 'matt.huntington@gmail.com';
```
Select all rows from the user table where *either* the name column is set to 'Matt' OR the email column is set to matt.huntington@gmail.com
```sql
SELECT * FROM users WHERE name = 'Matt' OR email = 'matt.huntington@gmail.com';
```
Select all rows from the user table where the age column is set to 36
```sql
SELECT * FROM users WHERE age = 36;
```
Select all rows from the user table where the age column is not set to 16
```sql
SELECT * FROM users WHERE age != 16;
```
Select all rows from the user table where the age column is greater than 26
```sql
SELECT * FROM users WHERE age > 26;
```
Select all rows from the user table where the age column is less than 46
```sql
SELECT * FROM users WHERE age < 46;
```
Select all rows from the user table where the age column is less than or equal to 36
```sql
SELECT * FROM users WHERE age <= 36;
```
Select all rows from the user table where the age column is greater than or equal to 36
```sql
SELECT * FROM users WHERE age >= 36;
```
Select all rows from the user table where the age column has no value
```sql
SELECT * FROM users WHERE age IS NULL;
```
Select all rows from the user table where the age column has any value
```sql
SELECT * FROM users WHERE age IS NOT NULL;
``` ```
## Update the table ## Update the table
Update the users table. Set the name column to 'Matthew' for every row that has the id column set to 1. **VERY IMPORTANT** If you do not specify a `WHERE` condition, or in some other way limit it, the query will alter **every row** in your table. **WATCH OUT!!**
```sql ```sql
UPDATE users SET name = 'Matthew' WHERE id = 1; -- update the users table. Set the name column to 'Matthew' for every row that has the id column set to 1 UPDATE users SET name = 'Matthew' WHERE id = 1;
``` ```
## Delete from table ## Delete from table
Delete all rows from the users table that have the id column set to 1. **VERY IMPORTANT** If you do not specify a `WHERE` condition, or in some other way limit it, the query will delete **every row** in your table. **WATCH OUT!!**
```sql ```sql
DELETE FROM users WHERE id = 1; -- delete all rows from the users table that have the id column set to 1 DELETE FROM users WHERE id = 1;
``` ```

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