SQL
Computer Science: OCR A Level, topic 3.2.7
Structured Query Language
A database is a structured collection of data. Structured query language (SQL) is a language used to query this data.
SQL
- SQL is a language that can tell databases what to do.
- SQL can be used for selecting, inserting, updating, and deleting data.
Select statements
- A SELECT statement searches for and returns data. E.g:
- SELECT * FROM table_name;
- The * character tells the database to return all fields.
- The * character can be replaced by specific fields. E.g:
- SELECT name FROM users;
Where clause
- Sometimes we don't want to return data for all records.
- We can filter the data using a where clause as follows:
- SELECT * FROM users WHERE ID=3;
- The above line would only return a user's data where they have an ID of 3.
Wildcards
- Sometimes we don't know the exact value we want to use in a where clause.
- We can use wildcards to find records which match some sort of pattern.
- The % symbol can be used to represent anything.
- For example, if we want to find any names starting with 'Ba' then we could query:
- SELECT name FROM users WHERE name LIKE "Ba%";
Test yourself on SQL
What does the * wildcard mean in SQL?