[SQL 배우기] Section 2. SQL Statement Fundamentals

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SELECT: most common statement used to retrieve information from a table

• SELECT column_name FROM table_name
  • using * instead of the column name retrieves all the columns
  • separate column names by a comma for multiple columns
• using capital letters for SQL keywords helps with visualization

 

SELECT DISTINCT: used to return distinct values in columns

• SELECT DISTINCT column_name FROM table_name
  • parenthesis can be used around column name for better clarity

 

COUNT: returns the number of input rows that match a specific condition of a query

• SELECT COUNT (column_name/results) FROM table_name;
  • needs parenthesis
• SELECT COUNT(*) FROM table_name
  • returns the number of rows in a table
• more useful when used with keywords like DISTINCT

 

SELECT WHERE: allows to specify conditions on columns for the rows to be returned (filtering

• SELECT column_names FROM table_names WHERE conditions
• Comparison operators
  • =,>,<,>=,<=, (<> or !=)
• Logical operators
  • AND, OR, NOT

 

ORDER BY: sort rows based on a column value (ascending or descending)

• SELECT columns FROM table ORDER BY columns ASC/DESC

 

LIMIT: limit the number of rows returned for a query

• LIMIT num_of_rows
• only viewing a few rows to get an idea of the table
• useful with ORDER BY
• goes to the end of the query

 

BETWEEN: used to match a value against a range of values

• value BETWEEN low AND high
  • inclusive
  • can be used with dates when it is in YYYY-MM-DD format

 

IN: creates a condition to check if a value is included in a list of options

• value IN (option1, option2, option3, option_n)

 

LIKE: pattern matching with string data using wildcard characters

• %
  • matches any sequence of characters
  • putting % in the back of the character is looking for matching in the beginning, and vice versa
• _
  • matches any single character (replacing a single character)
  • can use multiple underscores

 

ILIKE: case-insensitive version of LIKE