大约有 43,000 项符合查询结果（耗时：0.0377秒） [XML]
Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL?
...k around it from within psql by executing the DDL statement conditionally:
SELECT 'CREATE DATABASE mydb'
WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'mydb')\gexec
The manual:
\gexec
Sends the current query buffer to the server, then treats each column of each row of the query's outpu...
What is your favorite C programming trick? [closed]
.... you could make a string "object" like this:
struct X {
int len;
char str[1];
};
int n = strlen("hello world");
struct X *string = malloc(sizeof(struct X) + n);
strcpy(string->str, "hello world");
string->len = n;
here, we've allocated a structure of type X on the heap that is the...
Retrieve the maximum length of a VARCHAR column in SQL Server
...
Use the built-in functions for length and max on the description column:
SELECT MAX(LEN(DESC)) FROM table_name;
Note that if your table is very large, there can be performance issues.
share
|
im...
Spring Boot JPA - configuring auto reconnect
...1.3
spring.datasource.testOnBorrow=true
spring.datasource.validationQuery=SELECT 1
As djxak noted in the comment, 1.4+ defines specific namespaces for the four connections pools Spring Boot supports: tomcat, hikari, dbcp, dbcp2 (dbcp is deprecated as of 1.5). You need to check which connection po...
Is there a better way to dynamically build an SQL WHERE clause than by using 1=1 at its beginning?
... {2}", clause, appender, condition);
}
Use it like this
string query = "SELECT * FROM Table1 {0}";
string whereClause = string.Empty;
if (condition 1)
whereClause = AddCondition(whereClause, "AND", "Col=1");
if (condition 2)
whereClause = AddCondition(whereClause, "AND", "Col2=2");
str...
Rails raw SQL example
...
You can do this:
sql = "Select * from ... your sql query here"
records_array = ActiveRecord::Base.connection.execute(sql)
records_array would then be the result of your sql query in an array which you can iterate through.
...
Keeping it simple and how to do multiple CTE in a query
...s in one query, as well as reuse a CTE:
WITH cte1 AS
(
SELECT 1 AS id
),
cte2 AS
(
SELECT 2 AS id
)
SELECT *
FROM cte1
UNION ALL
SELECT *
FROM cte2
UNION ALL
SELECT *
FROM cte1
Note, however, that SQL Server may reevaluate t...
How to get the sizes of the tables of a MySQL database?
...he size of a table (although you need to substitute the variables first):
SELECT
table_name AS `Table`,
round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB`
FROM information_schema.TABLES
WHERE table_schema = "$DB_NAME"
AND table_name = "$TABLE_NAME";
or this query ...
Android getting value from selected radiobutton
... @Override
public void onClick(View v) {
// get selected radio button from radioGroup
int selectedId = radioGroup.getCheckedRadioButtonId();
// find the radiobutton by returned id
radioButton = (RadioButton) findViewById(selectedId);
...
Select parent element of known element in Selenium
I have a certain element that I can select with Selenium 1.
7 Answers
7
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