27 real Schema & DDL questions from the SQL bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is CREATE TABLE?
Junior
A.a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns
B.a DDL statement that defines a new relation by specifying its column names, data types, and constraints
C.a DDL statement that changes an existing table's structure, such as adding a column, dropping a column, or modifying a constraint
D.a rule that validates each row against a boolean condition and rejects any row for which the condition is false
5. Which term means: "a DDL statement that changes an existing table's structure, such as adding a column, dropping a column, or modifying a constraint"?
11. Which term means: "a constraint enforcing referential integrity by requiring a column's values to match an existing key in another (or the same) table"?
A.UNIQUE constraint — a rule guaranteeing no two rows share the same value in the specified column(s), while still permitting NULLs in most engines
B.UNIQUE constraint — a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns
C.UNIQUE constraint — a constraint enforcing referential integrity by requiring a column's values to match an existing key in another (or the same) table
D.UNIQUE constraint — a column clause supplying a fallback value automatically used when an insert omits that column
A.CHECK constraint — a rule guaranteeing no two rows share the same value in the specified column(s), while still permitting NULLs in most engines
B.CHECK constraint — a rule that validates each row against a boolean condition and rejects any row for which the condition is false
C.CHECK constraint — a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns
D.CHECK constraint — a column clause supplying a fallback value automatically used when an insert omits that column
A.NOT NULL — a column constraint that forbids the absence of a value, forcing every row to supply something for that column
B.NOT NULL — a rule guaranteeing no two rows share the same value in the specified column(s), while still permitting NULLs in most engines
C.NOT NULL — a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns
D.NOT NULL — a rule that validates each row against a boolean condition and rejects any row for which the condition is false
26. Which term means: "a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns"?
A.SERIAL — a column clause supplying a fallback value automatically used when an insert omits that column
B.SERIAL — a Postgres pseudo-type that auto-generates increasing integer keys, equivalent in purpose to MySQL AUTO_INCREMENT and standard IDENTITY columns
C.SERIAL — a constraint identifying each row uniquely; it forbids duplicate values and forbids NULLs, and a table may have only one
D.SERIAL — a DDL statement that changes an existing table's structure, such as adding a column, dropping a column, or modifying a constraint
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