Databases are at the heart of most modern web applications, and PostgreSQL is one of the most popular relational database systems out there. One powerful feature of PostgreSQL—and SQL in general—is the CASE expression. It brings an element of conditional logic to the world of querying, allow...
Dans ce tutoriel, vous apprendrez àécrire des requêtes conditionnelles dans PostgreSQL en utilisant l'expression conditionnelle CASE de PostgreSQL. Actualisé 16 janv. 2025 · 7 min de lecture Contenu Mise en place d'une base de données PostgreSQL en local Exploration de la countries table...
importpsycopg2importpandasaspdfromsqlalchemyimportcreate_engine,text# 连接数据库取数engine=create_engine('postgresql+psycopg2://postgres:123456@127.0.0.1:5432/sql_advanced')df=pd.read_sql_query('SELECT * FROM poptbl',engine)# 创建一个字典,用来映射pref_name和districtdistrict_map={'德岛':'九州','...
importpandasaspddf=pd.read_sql_query('SELECT * FROM GREATESTS',engine)# 字典映射sort_dict={'B':1,'A':2,'D':3,'C':4,'E':5}df['neworder']=df['key_name'].map(sort_dict)# 按照neworder排序df=df.sort_values('neworder')df=df[['key_name','neworder']]Df 输出如下: 至此我们...
statement to create or formulate a query/expression. It can be used with any statement or clause where an expression can be used, such as with a WHERE clause, with the SELECT statement, etc. This post has presented various examples to explain the usage of the case statement in PostgreSQL....
by Baji Shaik and Scott Mead on 11 AUG 2023 in Advanced (300), Amazon Aurora, Amazon RDS, PostgreSQL compatible, RDS for PostgreSQL Permalink Comments Share It’s important to be aware of the case sensitivity of text data in PostgreSQL when performing queries or comparisons to ensure that ...
Summary: in this tutorial, you will learn how to use the PostgreSQL CASE conditional expression to form conditional queries. The PostgreSQL CASE expression is the same as IF/ELSE statement in other programming languages. It allows you to add if-else logic to the query to form a powerful query...
Under such circumstances, there comes the need forcase-insensitivequeries. The case-insensitive queries will return the search results without bothering about the case. Let’s see how can we query the case-insensitive queries in PostgreSQL.
I want to insert data from mysql into a table in postgresql. I want to perform a WHERE NOT EXISTS statement for a particular id. # Source data: MySQL curr_msql.execute(''' SELECT code, subjectname FROM test_subj ''') # Target data: PostgreSQL for row in curr_msql: curr_psql.execut...
When you insert some records, notice that PostgreSQL will accept “duplicated terms”. INSERTINTOusers(name,username)VALUES('John Doe','john');INSERTINTOusers(name,username)VALUES('Doe, John','JOHN'); If you select all records with a query likeSELECT * FROM usersyou can see that you have...