Possible Duplicate:
In SQL, what s the difference between count(column) and count()?
Count() vs Count(1)
I have big tables which keep long texts for example email content or news. And my question is there any difference for performance for counting table rows :
SELECT COUNT(*) FROM table_name
SELECT COUNT(t.id) FROM table_name as t
谁更好? 或后者将采用最佳查询方法加以优化? 是否有这方面的文件?
它们不同。
COUNT(*) will retrieve all values (even the NULL values count).
COUNT(t.id) doesn t count the NULL values.
就业绩而言,这些指标相同(查询优化器是聪明的)。
彩票计划相同,但在测试中,使用率(略微)更快。
在指定一栏名时,没有考虑到面值。
I noticed that there were some threads with similar questions, and I did look through them but did not really get a convincing answer. Here s my question: The subquery below returns a Table with 3 ...
I m 查询Oracle 10g。 我有两张表格(样本数据见下文)。 i m 试图提取一些领域
We have a restaurant table that has lat-long data for each row. We need to write a query that performs a search to find all restaurants within the provided radius e.g. 1 mile, 5 miles etc. We have ...
What are some cool SQL shorthands that you know of? For example, something I learned today is you can specify to group by an index: SELECT col1, col2 FROM table GROUP BY 2 This will group by col2
I have an array of output from a database. I am wondering what the cleanest way to filter the values is example array Array ( [0] => Array ( [title] => title 1 ...
we have a table in an Oracle Database which contains a column with the type Char(3 Byte). Now we use a parameterized sql to select some rows with a DBNull.Value and it doesn t work: OracleCommand ...
I have a SQL-statement like this: SELECT name FROM users WHERE deleted = 0; How can i create a result set with a running number in the first row? So the result would look like this: 1 Name_1 2 ...
I’m developing an application dedicated to generate statistical reports, I would like that user after saving their stat report they save sql queries too. To do that I wrote the following module: ...