which three are true about scalar subquery expressions?
A. They cannot be used in group by clauses.
B. A scalar subquery expression that returns zero rows evaluates to zero.
C. They can be nested.
D. A scalar subquery expression that returns zero rows evaluates to null.
E. They can be used as default values for columns in a create table statement.
F. They cannot be used in the values clause of an insert statement.
Answer: ADF
Explanation:
固定的理論知識，查看官方文檔
A. 它們不能在group by子句中使用，正確
B. 返回0行的標量子查詢表達式計算結果為0，錯誤，結果為null
C. 可以嵌套，錯誤
D. 返回零行的標量子查詢表達式計算結果為null，正確
E. 它們可以在create table語句中用作列的默認值，錯誤，不可作為默認值
F. 它們不能在insert語句的values子句中使用，正確
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