IT技能面试题附答案（国外英文资料）.docVIP

IT技能面试题附答案（国外英文资料） A, multiple choice (1) there are 2 rows of data in table T1, 3 rows in T2, and execution of SQL statements Select a. * from T1 a, T2 b, the number of rows returned is ______ A, 2 rows B, 3 lines C, 5 lines D, 6 rows The multi-table query does not specify the connection condition, which leads to the occurrence of the cartesian product, which returns the number of rows in the rows of two tables, and returns six rows of records Review: the understanding of multi-table joins and cartesian products Answer: A, (2), known the completely same field definition of table T1 and T2, T1, T2, each have five different data in the T1 there are 2 data in tables T2, the statement select * from T1 union select * from T2 The number of rows returned is A, 8 lines B, 10 lines C, 3 lines D, 12 lines After the second question the UNION links in the table will filter out duplicate records, so after links in the table of the result set generated by sorting operation, remove duplicate records and return the result. Review: the understanding of the UNION Answer: A, (3) the given table T1 has the field ID, the CourseID, and the Score, and the data is ID CourseID Score 3 1, 90 2 1 85 2 2 90 3 2, 80 The statement select id, sum (ScorE) from T1 group by id results in A, ID sum (ScorE) -- -- 3, 170 Two hundred and seventy-five So, B, ID sum (ScorE) -- -- Two hundred and seventy-five 3, 170 So, C, ID sum (ScorE) -- -- 2, 170 3175 So, D, and Im going to have a ScorE. -- -- 3175 2, 170 The third question, GROUP BY, GROUP BY the ID field, and the ScorE for the same field of the ID, the GROUP BY automatically collates the result set so the answer is choice B Review: group by understanding Answer: B (4), phone number table t_phonebook containing 1 million data, which created a unique index on PhoneNo number field, and telephone number all is composed of Numbers, the phone number of the pier to statistics for 321, the number of the following is written in the execution speed of the slow