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Code&Data Insights
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The Art of Statistics: Learning from Data by David Spiegelhalter =>David Spiegelhalter is a prominent British statistician who provides numerous examples from his professional experience in the field of statistics. He endeavors to explain these concepts in an accessible way, without relying on mathematical formulas. 2학년때 probability and statistics 과목을 들었는데, 감이 안잡혀서 책을 읽었다. 다양한 예시를 줘서 전체적인 통계학의 개..
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Schemas and Instances - Databases instance: the current content of the DB - Databases schema: the structure of the data(relations/classes) -> Relation(table) is as a set or tuple! What is the meaning of Data Independence?? : the ability to modify definition of schema at one level with little or no effect on the schema at a high level - Logical data independence: adding new fields to a record or ..
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What is a Database? : a collection (Not a random pile of data) of data that exists over a long period time. DBMS : a complex software package developed to store and manage databases è Mysql, mongoDB, … è Provide convenient, efficient, and secure access and manipulation of large amounts of data è Controls access to shared data from multiple, simultaneous users with properties Atomicity, Consisten..
Key difference between SQL Keys SQL keys are used to uniquely identify rows in a table. SQL keys can either be a single column or a group of columns. Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table. Super keys can contain redundant attributes that might not be important for identifying tuples. Candidate keys are a subset of Super keys. They cont..
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https://resumeworded.com/linkedin-review/linkedin-headline-examples-for-students Proven LinkedIn Headline Examples for StudentsHow to optimize your LinkedIn headline if you're a student An optimized LinkedIn headline can increase the number of views to your profile significantly. More views to your profile by the right people (e.g. hiring managers and recruiters) often means moreresumeworded.com..
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5. Give details of employees who worked in at least two different facilities. Details include employee’s first-name, last-name, start date, end date, facility name, role (nurse, doctor, etc.), Medicare card number, telephone-number, and email address. Results should be displayed sorted in ascending order by first name, then by last name, then by start date. QUERY) SELECT e.firstName, e.lastName..
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Inner Join : selects records that have matching values in both tables. => intersection of two tables SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name; Left Join SELECT column_name(s) FROM table1 LEFT JOIN table2 ON table1.column_name = table2.column_name; Right Join SELECT column_name(s) FROM table1 RIGHT JOIN table2 ..
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What is a NULL Value? : NULL value is a filed with no value. NULL is not value, it's just a place holder ** Therefore, we can't compare between NULL values! Null is unknown, so they can't be same ! null != null Can we test for NULL? : Yes, it's possible to test for using IS NULL & IS NOT NULL NULL Value with Groung and Aggregating : Nulls are counted when grouping, but ig..