Arrays with SQL - Day 3

LeetCode

• Subject: Searching for Insertion

Given a sorted array and a target value , find the target value in the array and return its index . If the target value does not exist in the array, returns the position where it will be inserted in order. Please use an O(log n) algorithm.

• Problem solving ideas

① First consider the case where the target number is the first or before the first number

②Consider the case where the target number is not in the array and after the last number

③ When considering the target number in the array or the position where it should be inserted in order

[ Knowledge points ] array, for loop, if judgment, break

•  result

public class LeetCodePrac {

	public static void main(String[] args) {
		int[] nums = { 1，2，4，5 };
		System.out.println(searchInsert(nums, -1));
	}

	public static int searchInsert(int[] nums, int target) {
		int index = -1;
		int len = nums.length;
        if (nums[0] >= target) {
			return 0;
		} else if (nums[len - 1] < target) {
			return len;
		}
		for (int i = 1; i < len; i++) {
			if (nums[i - 1] < target & nums[i] >= target) {
				index = i;
				break;
			}
		}
		return index;
	}

nowcoder

• Topic: Create an index idx_emp_no for the emp_no field of the salaries table above

The salaries table has been created, the index idx_emp_no is created for the emp_no field, the query emp_no is 10005, and the mandatory index is used .

CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));
create index idx_emp_no on salaries(emp_no);

INSERT INTO salaries VALUES(10005,78228,'1989-09-12','1990-09-12');
INSERT INTO salaries VALUES(10005,94692,'2001-09-09','9999-01-01');

• Problem solving ideas

【Knowledge points】

①SQL table query

SELECT * FROM <表名>

SELECT * FROM <表名> WHERE <字段名> [查询条件] <值>

② SQL forced index

SELECT * FROM <表名> FORCE INDEX (<索引名>) 
WHERE <字段名> [查询条件] <值>

• code

select * from salaries 
FORCE INDEX (idx_emp_no)
WHERE emp_no=10005