sql cheat sheet for interview code example

Example 1: sql cheat sheet

# Finding Data Queries

# SELECT: used to select data from a database
SELECT * FROM table_name;

# DISTINCT: filters away duplicate values and returns rows of specified column
SELECT DISTINCT column_name;

# WHERE: used to filter records/rows
SELECT column1, column2 FROM table_name WHERE condition;
SELECT * FROM table_name WHERE condition1 AND condition2;
SELECT * FROM table_name WHERE condition1 OR condition2;
SELECT * FROM table_name WHERE NOT condition;
SELECT * FROM table_name WHERE condition1 AND (condition2 OR condition3);
SELECT * FROM table_name WHERE EXISTS (SELECT column_name FROM table_name WHERE condition);

# ORDER BY: used to sort the result-set in ascending or descending order
SELECT * FROM table_name ORDER BY column;
SELECT * FROM table_name ORDER BY column DESC;
SELECT * FROM table_name ORDER BY column1 ASC, column2 DESC;
SELECT TOP: used to specify the number of records to return from top of table
SELECT TOP number columns_names FROM table_name WHERE condition;
SELECT TOP percent columns_names FROM table_name WHERE condition;

# Not all database systems support SELECT TOP. The MySQL equivalent is the LIMIT clause
SELECT column_names FROM table_name LIMIT offset, count;

# LIKE: operator used in a WHERE clause to search for a specific pattern in a column
# % (percent sign) is a wildcard character that represents zero, one, or multiple characters
# _ (underscore) is a wildcard character that represents a single character
SELECT column_names FROM table_name WHERE column_name LIKE pattern;

LIKE ‘a%’ # (find any values that start with “a”)
LIKE ‘%a’ # (find any values that end with “a”)
LIKE ‘%or%’ # (find any values that have “or” in any position)
LIKE ‘_r%’ # (find any values that have “r” in the second position)
LIKE ‘a_%_%’ # (find any values that start with “a” and are at least 3 characters in length)
LIKE ‘[a-c]%’ # (find any values starting with “a”, “b”, or “c”

# See more in the source link

Example 2: sql interview questions

/*SQL query to fetch duplicate records from a table .
Ans. In order to find duplicate records from the table, we can use GROUP BY on all the fields and then use the HAVING clause to return only those fields whose count is greater than 1 i.e. the rows having duplicate records.
*/ 
SELECT FullName, ManagerId, DateOfJoining, City, COUNT(*) FROM EmployeeDetails GROUP BY FullName, ManagerId, DateOfJoining, City HAVING COUNT(*) > 1;