select

Is SELECT WHERE [primary key] = [primary key value] O(1)?

由 本秂侑毒 提交于 2021-02-07 08:24:04
问题 Is it right to expect that, for the typical modern RDBMS, querying by one specific primary key is as fast as querying a hashtable by key? Or is there "actual work" done to traverse the table and track down the primary key value? That seems unthinkably wasteful, even if there are automatic indexes for primary keys. 回答1: Database operation involves access of secondary memory unit (Disk). And to achieve efficiency important is to reduce block access time(not operations). Complexity of Select

Dropdown onchange calling PHP Function

由 倖福魔咒の 提交于 2021-02-07 02:48:33
问题 What i'm attempting to do with the below code is call a PHP function from an dropdown menu. Is there a clean way of doing this? code: <html> <head> </head> <body> <?php function OnSelectionChange() { echo("OK IT WORKS"); } ?> <section> <select onchange="OnSelectionChange()"> <option value='' disabled selected>Assign Driver</option> <option value='4353'>Steve Jobs</option> <option value='3333'>Ian Wright</option> <option value='66666'>Mark James</option> </select> </section> </body> </html>

How to create a new column in a select query

由 我与影子孤独终老i 提交于 2021-02-06 09:42:57
问题 In MS Access, I want to insert a new column into the returned result of a select query. The new column has the same value for every row. For example, my select returns columns A, B and I want C to be the new column created by the select query: A B C ---------- a1 b1 c a2 b2 c a3 b3 c 回答1: select A, B, 'c' as C from MyTable 回答2: SELECT field1, field2, 'example' AS newfield FROM TABLE1 This will add a column called "newfield" to the output, and its value will always be "example". 回答3: It

How to create a new column in a select query

由 假如想象 提交于 2021-02-06 09:41:16
问题 In MS Access, I want to insert a new column into the returned result of a select query. The new column has the same value for every row. For example, my select returns columns A, B and I want C to be the new column created by the select query: A B C ---------- a1 b1 c a2 b2 c a3 b3 c 回答1: select A, B, 'c' as C from MyTable 回答2: SELECT field1, field2, 'example' AS newfield FROM TABLE1 This will add a column called "newfield" to the output, and its value will always be "example". 回答3: It

Break out of select loop?

由 时光毁灭记忆、已成空白 提交于 2021-02-05 20:19:57
问题 I'm trying to use a select in a loop to receive either a message or a timeout signal. If the timeout signal is received, the loop should abort: package main import ("fmt"; "time") func main() { done := time.After(1*time.Millisecond) numbers := make(chan int) go func() {for n:=0;; {numbers <- n; n++}}() for { select { case <-done: break case num := <- numbers: fmt.Println(num) } } } However, it doesn't seem to be stopping: $ go run a.go 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

PHP SQL STMT SELECT multiple LIKE ? is it possible?

由 拥有回忆 提交于 2021-02-05 12:20:29
问题 SELECT * FROM datatable WHERE Name LIKE ? OR Code LIKE ? OR Date LIKE ? OR Inserter LIKE ? AND ID = '2' There is an error in php sql connection: mysqli_stmt::bind_param(): Number of variables doesn't match number of parameters in prepared statement in Here is the error code, I am using stmt->prepare, stmt->execute and so on in php. This works fine with just one LIKE ? (WHERE Name LIKE ? AND ID = '2'). How can I replace or solve this problem? The real code if ($stmt = $db->prepare($SearchQuery

Every derived table must have its own alias - error when using multiple SELECT statements

由 大憨熊 提交于 2021-02-05 09:30:35
问题 I'm trying to use multiple SELECT statements in a query to get data from the database but I get an error. The query is: SELECT * FROM (SELECT * FROM players WHERE lid = 0) WHERE NOT EXISTS (SELECT * FROM players WHERE lid = 1) The error is get is: Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1248 Every derived table must have its own alias' I tried changing my query to SELECT * FROM (SELECT * FROM players WHERE lid = 0) WHERE

Selecting multiple array elements

由 这一生的挚爱 提交于 2021-02-05 09:12:09
问题 Is there a way in PHP to select multiple array elements at once, e.g. such that in a for loop, $i = size of first set to be selected, and then subsequent increments represent selecting the next set of that size, from an array - ? Thanks! 回答1: I.e. instead of just looping through one array element at a time, but to loop through selected pairs instead (e.g. 3 elements, and then to do something to those 3). there are many ways to do it. one would be $arr = array(1,2,3,4,5,6,7,8,9); $new = array

Selecting multiple array elements

由 末鹿安然 提交于 2021-02-05 09:12:07
问题 Is there a way in PHP to select multiple array elements at once, e.g. such that in a for loop, $i = size of first set to be selected, and then subsequent increments represent selecting the next set of that size, from an array - ? Thanks! 回答1: I.e. instead of just looping through one array element at a time, but to loop through selected pairs instead (e.g. 3 elements, and then to do something to those 3). there are many ways to do it. one would be $arr = array(1,2,3,4,5,6,7,8,9); $new = array

Get Employees Who Are Below Average Salary After A Raise

由 与世无争的帅哥 提交于 2021-02-05 09:03:00
问题 I need to get fname, lname, salary of employees who are $400.00 below the average salary even after geting a 10% salary raise. I'm able to get employees who's salary is below the average salary, but am unsure how to get those who are $400 below after a raise. I'm using MySQL. Thank you. select AVG(salary) from employee; #gives me the average salary select Fname, Lname, Salary, 1.10*Salary as NewSalary from employee; #gives me names, old salary and salary raised. This gives me the employees
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