DataBeat Interview Questions, Process, and Tips

Sql concepts and sql Queries

Q1. Difference between where and having
Ans. 
WHERE is used to filter rows before grouping, HAVING is used to filter groups after grouping.
• WHERE is used with SELECT statement to filter rows based on a condition

• HAVING is used with GROUP BY statement to filter groups based on a condition

• WHERE is applied before grouping, HAVING is applied after grouping

• Example: SELECT * FROM table_name WHERE column_name = 'value'

• Example: SELECT column_name, COUNT(*) FROM table_name G
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Q2. Difference between delete and truncate
Ans. 
Delete removes rows one by one, while truncate removes all rows at once.
• Delete is a DML command, while truncate is a DDL command

• Delete can be rolled back, while truncate cannot be rolled back

• Delete triggers delete triggers, while truncate does not trigger any triggers

• Delete is slower than truncate for large tables

• Example: DELETE FROM table_name WHERE condition;

• Example: TRUNCATE TABLE table_name;
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Q3. What is primary key and foreign key
Ans. 
Primary key uniquely identifies each record in a table, while foreign key establishes a link between two tables.
• Primary key ensures each record is unique

• Foreign key establishes a relationship between tables

• Primary key can be a single column or a combination of columns

• Foreign key references the primary key of another table
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Q4. Query Execution order
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Q5. What we consider for creating table
Ans. 
When creating a table, factors to consider include data types, column names, primary keys, relationships, and constraints.
• Consider the data types for each column (e.g. integer, text, date)

• Choose appropriate column names that are descriptive and easy to understand

• Define primary keys to uniquely identify each row

• Establish relationships between tables using foreign keys

• Set constraints to enforce data integrity (e.g. uniqu
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Q1. Explain about joins?
Ans. 
Joins are used in databases to combine rows from two or more tables based on a related column between them.
• Joins are used to retrieve data from multiple tables in a single query.

• Common types of joins include inner join, left join, right join, and full outer join.

• Inner join returns only the matching rows between the tables.

• Left join returns all rows from the left table and the matching rows from the right table.

• Right jo...read more
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