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Questions and Answers
What does the SQL functionCONCAT do?
What does the SQL functionCONCAT do?
Which type of SQL statement is used to create a new database, table, or index?
Which type of SQL statement is used to create a new database, table, or index?
What is the purpose of the HAVING clause in a SQL query?
What is the purpose of the HAVING clause in a SQL query?
What is the result of the SQL query SELECT COUNT(*) FROM table_name;
What is the result of the SQL query SELECT COUNT(*) FROM table_name;
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What type of SQL join returns all rows from both tables, with null values in the columns where there are no matches?
What type of SQL join returns all rows from both tables, with null values in the columns where there are no matches?
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What is the purpose of the GROUP BY clause in a SQL query?
What is the purpose of the GROUP BY clause in a SQL query?
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What is the main purpose of using a subquery in SQL?
What is the main purpose of using a subquery in SQL?
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What is the data type of the value returned by the NOW() function in SQL?
What is the data type of the value returned by the NOW() function in SQL?
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Study Notes
SQL Basics
- SQL stands for Structured Query Language
- Used to manage and manipulate data in relational databases
- Consists of a series of commands or statements to perform specific tasks
Data Types
- Integer (int): whole numbers, e.g. 1, 2, 3
- String (varchar, char): characters, e.g. 'hello', "hello"
- Date (date, datetime): dates and timestamps, e.g. '2022-01-01', '2022-01-01 12:00:00'
- Boolean (bool): true or false values
SQL Statements
DDL (Data Definition Language)
- CREATE: create a new database, table, or index
- ALTER: modify an existing database, table, or index
- DROP: delete a database, table, or index
DML (Data Manipulation Language)
- INSERT: add new data to a table
- UPDATE: modify existing data in a table
- DELETE: delete data from a table
DQL (Data Query Language)
- SELECT: retrieve data from a table
- FROM: specify the table(s) to retrieve data from
- WHERE: filter data based on conditions
- GROUP BY: group data based on one or more columns
- HAVING: filter grouped data based on conditions
- ORDER BY: sort data in ascending or descending order
- LIMIT/OFFSET: limit the number of rows returned
SQL Functions
- Aggregate functions:
- SUM: calculate the total value of a column
- AVG: calculate the average value of a column
- MAX: return the maximum value of a column
- MIN: return the minimum value of a column
- COUNT: return the number of rows
- String functions:
- CONCAT: concatenate strings
- LENGTH: return the length of a string
- LOWER/UPPER: convert strings to lowercase/uppercase
- Date functions:
- NOW(): return the current date and time
- DATE_FORMAT: format a date string
SQL Joins
- INNER JOIN: combine two tables based on a common column
- LEFT JOIN: combine two tables, returning all rows from the left table
- RIGHT JOIN: combine two tables, returning all rows from the right table
- FULL OUTER JOIN: combine two tables, returning all rows from both tables
SQL Subqueries
- A query nested inside another query
- Used to retrieve data that meets certain conditions
- Can be used in SELECT, FROM, WHERE, and HAVING clauses
SQL Basics
- SQL stands for Structured Query Language and is used to manage and manipulate data in relational databases
- Consists of a series of commands or statements to perform specific tasks
Data Types
- Integer (int): whole numbers, e.g. 1, 2, 3
- String (varchar, char): characters, e.g. 'hello', "hello"
- Date (date, datetime): dates and timestamps, e.g. '2022-01-01', '2022-01-01 12:00:00'
- Boolean (bool): true or false values
SQL Statements
DDL (Data Definition Language)
- CREATE: create a new database, table, or index
- ALTER: modify an existing database, table, or index
- DROP: delete a database, table, or index
DML (Data Manipulation Language)
- INSERT: add new data to a table
- UPDATE: modify existing data in a table
- DELETE: delete data from a table
DQL (Data Query Language)
- SELECT: retrieve data from a table
- FROM: specify the table(s) to retrieve data from
- WHERE: filter data based on conditions
- GROUP BY: group data based on one or more columns
- HAVING: filter grouped data based on conditions
- ORDER BY: sort data in ascending or descending order
- LIMIT/OFFSET: limit the number of rows returned
SQL Functions
Aggregate Functions
- SUM: calculate the total value of a column
- AVG: calculate the average value of a column
- MAX: return the maximum value of a column
- MIN: return the minimum value of a column
- COUNT: return the number of rows
String Functions
- CONCAT: concatenate strings
- LENGTH: return the length of a string
- LOWER/UPPER: convert strings to lowercase/uppercase
Date Functions
- NOW(): return the current date and time
- DATE_FORMAT: format a date string
SQL Joins
- INNER JOIN: combine two tables based on a common column
- LEFT JOIN: combine two tables, returning all rows from the left table
- RIGHT JOIN: combine two tables, returning all rows from the right table
- FULL OUTER JOIN: combine two tables, returning all rows from both tables
SQL Subqueries
- A query nested inside another query
- Used to retrieve data that meets certain conditions
- Can be used in SELECT, FROM, WHERE, and HAVING clauses
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Description
Test your understanding of SQL fundamentals, including data types such as integers, strings, dates, and booleans, and SQL statements like DDL.
