Which option is true about SQL query?
Correct answer is option ‘A‘.
Which of the following is the correct order of occurrence in a typical SQL statement?
1) Which of the following is the correct order of occurrence in a typical SQL statement? “Where” always comes before “group by” and “having” always comes after “group by”.
Which query will output all rows from T1 and only matching rows from T2?
In short, the LEFT JOIN clause returns all rows from the left table (T1) and matching rows or NULL values from the right table (T2).
Which is true about the primary key Mcq?
The primary key is a single or combination of the field that identifies each record in a table uniquely. It cannot take a NULL value. A table can have only one primary key.
What is the where clause in SQL?
The SQL WHERE Clause
The WHERE clause is used to filter records. It is used to extract only those records that fulfill a specified condition.
How many tables can be join in SQL query?
Theoretically, there is no upper limit on the number of tables that can be joined using a SELECT statement. (One join condition always combines two tables!) However, the Database Engine has an implementation restriction: the maximum number of tables that can be joined in a SELECT statement is 64.
Why use full join in SQL?
SQL full outer join is used to combine the result of both left and right outer join and returns all rows (don’t care its matched or unmatched) from the both participating tables.
Which one of the following is correct syntax for insert statement?
There are two basic syntax of INSERT INTO statement is as follows: INSERT INTO TABLE_NAME (column1, column2, column3,… columnN)] VALUES (value1, value2, value3,… valueN);
What is the correct order of clauses in select statement?
The FROM clause: First, all data sources are defined and joined. The WHERE clause: Then, data is filtered as early as possible. The CONNECT BY clause: Then, data is traversed iteratively or recursively, to produce new tuples.
Can you join without on SQL?
Omit the ON clause from the JOIN statement
In MySQL, it’s possible to have a JOIN statement without ON as ON is an optional clause. You can just simplly JOIN two tables like this: SELECT * FROM table_a JOIN table_b; It will match each row from table_a to every row in table_b .
Can you join without on clause?
Any JOIN without an ON clause is a CROSS JOIN. The LEFT JOIN is an outer join, which produces a result set with all rows from the table on the “left” (t1); the values for the columns in the other table (t2) depend on whether or not a match was found. … JOINs can be concatenated to read results from three or more tables.
Can LEFT join increase row count?
Left joins can increase the number of rows in the left table if there are multiple matches in the right table. … Ideally, you’d be able to handle multiple matches on the join inside of the EG Join Tables layout directly.
Can primary key be changed?
The PRIMARY KEY constraint specifies that the constrained columns’ values must uniquely identify each row. … You can change the primary key of an existing table with an ALTER TABLE … ALTER PRIMARY KEY statement, or by using DROP CONSTRAINT and then ADD CONSTRAINT in the same transaction.
What are the keys used in DBMS?
There are broadly seven types of keys in DBMS:
- Primary Key.
- Candidate Key.
- Super Key.
- Foreign Key.
- Composite Key.
- Alternate Key.
- Unique Key.