Which of the following is a valid SQL statement?

Question

Which of the following is a valid SQL statement?​

BlackTom AI · Accepted Answer

Question: Which of the following is a valid SQL statement?

Option 1: 'CREATE TABLE newname (colA NUMBER, colB DATE);' 
- This is a standard CREATE TABLE statement that defines a new table named newname with two columns: colA of type NUMBER and colB of type DATE. It follows typical SQL syntax for explicit column definitions, and is valid in many relational databases such as Oracle and PostgreSQL. The parentheses correctly enclose the column definitions and their data types, and there is a semicolon to terminate the statement.

Option 2: 'CREATE TABLE newname as SELECT * FROM books;' 
- This resembles a CREATE TABLE ... AS SELECT statement, which is valid in several SQL dialects (e.g., Oracle, PostgreSQL, SQL Server supports similar constructs). However, the exact ordering and capitalization are not the issue here; the potential pitfall is that in some contexts you must use 'AS' in uppercase and ensure there is a proper SELECT list and FROM clause. As written, this could be valid in dialects that support CTAS (Create Table As Select). Depending on the dialect, the absence of a semicolon or case sensitivity typically does not invalidate it, but dialect compatibility can differ. In many test contexts, this form is considered valid.

Option 3: 'CREATE TABLE newname (colA, colB);' 
- This attempts to declare a table with two columns but omits data types for colA and colB. SQL requires each column to have an associated data type (e.g., NUMBER, VARCHAR, DATE). Without types, this statement is syntactically invalid in almost all databases.

Option 4: 'CREATE TABLE newname (colA DATE, colB VARCHAR2(3);' 
- This has a syntax error: a missing closing parenthesis for the column list. Additionally, VARCHAR2(3) is Oracle-specific, but the primary issue here is the unmatched parentheses, which makes the statement invalid regardless of dialect.

Summary of validity considerations:
- Option 1 provides explicit column definitions with data types and proper punctuation, a typical valid form across many systems. 
- Option 2 can be valid as a CTAS statement in dialects that support 'CREATE TABLE ... AS SELECT', but its validity can be dialect-dependent. 
- Option 3 lacks required data types for the columns, making it invalid.
- Option 4 has a punctuation error (missing closing parenthesis), making it invalid.

If you must pick a single universally valid statement across common SQL dialects, Option 1 is the safest and most universally accepted choice. The other options either rely on dialect-specific CTAS behavior or contain syntactic errors.

Which of the following is a valid SQL statement?单项选择题

类似问题