exists

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Performance Comparation Between sql SELECT NULL and SELECT 1

Which one is better for performance IF开发者_Python百科 EXISTS(Select null from table) or IF EXISTS(Select 1 from table)[详细]

2023-02-08 17:11 分类：问答
Java file exists at URL

Does anybody know a reliable method for seeing if a file exists at a URL, in Java? 开发者_如何学Python[详细]

2023-02-06 14:11 分类：问答
PHP if a table table row exists

In PHP, is there a way of making the following statement to check if a row exists? If \"the table cases has a \"passenger\" field with the value of 4 WHERE case= \'$case\'开发者_如何转开发 {[详细]

2023-02-06 00:30 分类：问答
SQL EXISTS performance

I understand that SQL EXISTS checks for the existence o开发者_运维知识库f rows, however does it evaluate the entire expression? So for example, would something like this:[详细]

2023-02-05 18:25 分类：问答
count rows in joined table but display 0 if no rows exist - mysql

The response header table is a joined table which is counted to display responses to a particular survey. If there are no rows, hence no responses, I want the count to display 0. But instead it is ski[详细]

2023-02-04 11:40 分类：问答
CodedUI null reference exception even when object exists

I have created a coded ui test that checks something in my software. It worke开发者_JAVA百科d fine, but now I keep getting null reference exception when I try to interact with my UITestControls (that[详细]

2023-02-04 05:27 分类：问答
python: check if variable is defined and return its value or return other value

I am trying to use this code result = arr[\'key1\'] or arr[\'key2\'] or arr[\'key3\'] explanation: I want to have value in result from either or dict keys .. the availability of keys depends on th[详细]

2023-02-01 10:10 分类：问答
check file exist with php isn't working, need help

Please advise me, what wrong with my following code: <a href=\"<?php echo $_url; ?>\" title=\"<?php echo $_name; ?>\">[详细]

2023-01-31 16:43 分类：问答
How can I modify the following code to have the same results with "exists"?(SQL)

I have been trying for hours but I can\'t think of anything as exists only returns boolean and every time I am trying to use exists I either get back the entire list of results or none.[详细]

2023-01-30 09:13 分类：问答
Python different functions depending on input

I wrote a program to solve the problems for my physics chapter which takes all the given data and does everything it can with it. I used a long string of if statements to check which functions are saf[详细]

2023-01-29 18:46 分类：问答