大约有 2,000 项符合查询结果（耗时：0.0196秒） [XML]
PostgreSQL Autoincrement
...any other integer data type, such as smallint.
Example :
CREATE SEQUENCE user_id_seq;
CREATE TABLE user (
user_id smallint NOT NULL DEFAULT nextval('user_id_seq')
);
ALTER SEQUENCE user_id_seq OWNED BY user.user_id;
Better to use your own data type, rather than user serial data type.
...
Programmatically creating Markdown tables in R with KnitR
...hwriter)
set.seed(9850104)
my.df <- data.frame(Var1=sample(x=c("Apple","Orange","Banana"),size=40,replace=TRUE),
Var2=sample(x=c("Dog","Cat","Bunny"),size=40,replace=TRUE))
tbl1 <- table(my.df$Var1,my.df$Var2)
tbl1 <- cbind(tbl1,rowSums(tbl1))
tbl1 <- rbind(tbl1,col...
SELECT DISTINCT on one column
...), product varchar(15))
insert into @TestData values (1 , 'FOO-23' ,'Orange')
insert into @TestData values (2 , 'BAR-23' ,'Orange')
insert into @TestData values (3 , 'FOO-24' ,'Apple')
insert into @TestData values (4 , 'FOO-25' ,'Orange')
--basically the same as @Aaron Alton...
Joining three tables using MySQL
...
SELECT *
FROM user u
JOIN user_clockits uc ON u.user_id=uc.user_id
JOIN clockits cl ON cl.clockits_id=uc.clockits_id
WHERE user_id = 158
share
|
improve this answer
...
Index on multiple columns in Ruby on Rails
... its columns in sequence starting at the beginning. i.e. if you index on [:user_id, :article_id], you can perform a fast query on user_id or user_id AND article_id, but NOT on article_id.
Your migration add_index line should look something like this:
add_index :user_views, [:user_id, :article_id...
How do I retrieve the number of columns in a Pandas data frame?
...import pandas as pd
df = pd.DataFrame({"pear": [1,2,3], "apple": [2,3,4], "orange": [3,4,5]})
len(df.columns)
3
share
|
improve this answer
|
follow
|
...
How to get ID of the last updated row in MySQL?
...sers set status = 'processing' where status = 'pending'
and last_insert_id(user_id)
limit 1
The addition of last_insert_id(user_id) in the where clause is telling MySQL to set its internal variable to the ID of the found row. When you pass a value to last_insert_id(expr) like this, it ends up ret...
Create unique constraint with null columns
... two partial indexes:
CREATE UNIQUE INDEX favo_3col_uni_idx ON favorites (user_id, menu_id, recipe_id)
WHERE menu_id IS NOT NULL;
CREATE UNIQUE INDEX favo_2col_uni_idx ON favorites (user_id, recipe_id)
WHERE menu_id IS NULL;
This way, there can only be one combination of (user_id, recipe_id) whe...
C# SQL Server - Passing a list to a stored procedure
...S ('Apple')
INSERT INTO @list VALUES ('Banana')
INSERT INTO @list VALUES ('Orange')
-- Alternatively, you can populate @list with an INSERT-SELECT
INSERT INTO @list
SELECT Name FROM Fruits
EXEC sp_UseStringList @list
s...
Find and replace with sed in directory and sub directories
I run this command to find and replace all occurrences of 'apple' with 'orange' in all files in root of my site:
7 Answers
...