大约有 40,000 项符合查询结果（耗时：0.0333秒） [XML]
How to select the row with the maximum value in each group
...
Here's a data.table solution:
require(data.table) ## 1.9.2
group <- as.data.table(group)
If you want to keep all the entries corresponding to max values of pt within each group:
group[group[, .I[pt == max(pt)], by=Subject]$V1]
# ...
How do I do a bulk insert in mySQL using node.js
...Ragnar123 led me to making this function:
function bulkInsert(connection, table, objectArray, callback) {
let keys = Object.keys(objectArray[0]);
let values = objectArray.map( obj => keys.map( key => obj[key]));
let sql = 'INSERT INTO ' + table + ' (' + keys.join(',') + ') VALUES ?';
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Sorting rows in a data table
We have two columns in a DataTable , like so:
12 Answers
12
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PHP: How to generate a random, unique, alphanumeric string for use in a secret link?
...unctions, then we can generate highly reliable unique strings. Here is the table showing my research data:
Update:
I created a simple Heroku app using these functions that returns the token as a JSON response. The app can be accessed at https://uniquestrings.herokuapp.com/api/token?length=15
I hope...
How to test an SQL Update statement before running it?
...man/5.0/en/commit.html
For example:
START TRANSACTION;
SELECT * FROM nicetable WHERE somthing=1;
UPDATE nicetable SET nicefield='VALUE' WHERE somthing=1;
SELECT * FROM nicetable WHERE somthing=1; #check
COMMIT;
# or if you want to reset changes
ROLLBACK;
SELECT * FROM nicetable WHERE somthing=1...
How do I update if exists, insert if not (AKA “upsert” or “merge”) in MySQL?
... @blub: If you create a unique key on geb and topic it will work (ALTER TABLE table ADD UNIQUE geb_by_topic (geb, topic)).
– chaos
Aug 2 '09 at 13:43
1
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postgresql return 0 if returned value is null
...al question).
There are two distinct "problems" here, the first is if a table or subquery has no rows, the second is if there are NULL values in the query.
For all versions I've tested, postgres and mysql will ignore all NULL values when averaging, and it will return NULL if there is nothing to ...
PostgreSQL: How to change PostgreSQL user password?
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The user is an object, not a string. Compare with ALTER TABLE "table_name" or even SELECT * FROM "table_name". You couldn't use single quotes in these contexts with tables, and it's the same with users/roles.
– P Daddy
Apr 13 '16 at 5:11
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What MySQL data type should be used for Latitude/Longitude with 8 decimal places?
...types and Point is a single-value type which can be used. Example:
CREATE TABLE `buildings` (
`coordinate` POINT NOT NULL,
/* Even from v5.7.5 you can define an index for it */
SPATIAL INDEX `SPATIAL` (`coordinate`)
) ENGINE=InnoDB;
/* then for insertion you can */
INSERT INTO `buildings`
(...
What does “exec sp_reset_connection” mean in Sql Server Profiler? [duplicate]
...llocated memory
owned by the connection
Clears any work or temporary
tables that are created by the
connection
Kills all global cursors owned by the
connection
Closes any open SQL-XML handles that are open
Deletes any open SQL-XML related work tables
Closes all system tables
Clo...