Querying

Querying is the process of asking questions of data. Querying makes use of keys primary and foreign within tables.

Useful Links

• CS50 SQL Course

SQL Commands and Examples

Basic SELECT Statement:

  SELECT * FROM longlist; -- Retrieves all data
  ```
 
```sql
  SELECT title FROM longlist; -- Retrieves book titles
  ```
 
```sql
  SELECT title, author FROM longlist; -- Retrieves titles and authors
  ```
 
**Using LIMIT**:
```sql
  SELECT title FROM longlist LIMIT 10; -- Retrieves the first 10 rows

   SELECT title FROM longlist LIMIT 5; -- Retrieves the first 5 rows
   ```
 
**Filtering with WHERE**:
```sql
   SELECT title, author FROM longlist WHERE year = 2023; -- Retrieves books from 2023
   ```
 
**Not Equals**:
  ```sql
     SELECT title, format FROM longlist WHERE format != 'hardcover';
     ```
     
  ```sql
     SELECT title, format FROM longlist WHERE format <> 'hardcover';
     ```
**NOT Keyword**:
  ```sql
     SELECT title, format FROM longlist WHERE NOT format = 'hardcover';
     ```
 
**Combining Conditions**:
 - Future lessons will cover more complex conditions, such as filtering by multiple years.
 
### Good Practices
**Capitalization**: 
 - Use uppercase for SQL keywords for better readability.
 - Use lowercase for table and column names.
 
**Quotes**:
 - Use double quotes for SQL identifiers (table and column names).
 - Use single quotes for string values.
### Example of LIKE with Wildcards
```sql
SELECT "title" 
FROM "longlist" 
WHERE "title" LIKE 'P_re';