大约有 6,100 项符合查询结果（耗时：0.0182秒） [XML]
For each row return the column name of the largest value
...partment name, rather than the number of roster counts, from the frequency table. A simple example below (column names = departments, row names = employee ids).
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MySQL主从服务器数据一致性的核对与修复 - 数据库(内核) - 清泛网 - 专注C/...
...一天被掩盖的问题会再次爆发出来。
Percona Toolkit里的pt-table-checksum和pt-table-sync可以搞定此类问题。它们的安装很简单，可以依照自己的操作系统选择下载rpm或者deb软件包来安装，当然也可以使用源代码来安装，不过要注意的是...
CHECK constraint in MySQL is not working
First I created a table like
8 Answers
8
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Numbering rows within groups in a data frame
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Use ave, ddply, dplyr or data.table:
df$num <- ave(df$val, df$cat, FUN = seq_along)
or:
library(plyr)
ddply(df, .(cat), mutate, id = seq_along(val))
or:
library(dplyr)
df %>% group_by(cat) %>% mutate(id = row_number())
or (the most memor...
MySQL Update Inner Join tables query
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Update:
Since you said the query yielded a syntax error, I created some tables that I could test it against and confirmed that there is no syntax error in my query:
mysql> create table business (business_id int unsigned primary key auto_increment, mapx varchar(255), mapy varchar(255)) engine=...
sql primary key and index
...ou may reach the desired optimization for a query.
For example you have a table with many columns but you are only querying ID, Name and Address columns. Taking ID as the primary key, we can create the following index that is built on ID but includes Name and Address columns.
CREATE NONCLUSTERED I...
Printing the value of a variable in SQL Developer
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DECLARE
CTABLE USER_OBJECTS.OBJECT_NAME%TYPE;
CCOLUMN ALL_TAB_COLS.COLUMN_NAME%TYPE;
V_ALL_COLS VARCHAR2(5000);
CURSOR CURSOR_TABLE
IS
SELECT OBJECT_NAME
FROM USER_OBJECTS
WHERE OBJECT_TYPE='TABLE'
AND OBJ...
django syncdb and an updated model
...ngo currently does not do this automatically. Your options are:
Drop the table from the database, then recreate it in new form using syncdb.
Print out SQL for the database using python manage.py sql (appname), find the added line for the field and add it manually using alter table SQL command. (Th...
Limiting the number of records from mysqldump?
...atabase
Of course, that would give you the first million rows from every table.
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Postgres dump of only parts of tables for a dev snapshot
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On your larger tables you can use the COPY command to pull out subsets...
COPY (SELECT * FROM mytable WHERE ...) TO '/tmp/myfile.tsv'
COPY mytable FROM 'myfile.tsv'
https://www.postgresql.org/docs/current/static/sql-copy.html
You shoul...