Bepaal de kolomnamen van een tabel

De videoles liet zien hoe je een SQL-query uitvoert. Je zag ook hoe je met SQL de kolomnamen van een Spark-tabel kunt bekijken. Dat is belangrijk, want in de praktijk worden relationele tabellen vaak zonder extra documentatie over het schemas van de tabel aangeleverd.

Raadpleeg gerust de dia's rechts van de console als je even niet meer weet hoe iets in de video werd gedaan.

Deze oefening maakt deel uit van de cursus

Introductie tot Spark SQL in Python

Cursus bekijken

Oefeninstructies

Gebruik een DESCRIBE-query om de namen en types van de kolommen in de tabel schedule te bepalen.

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Inspect the columns in the table schedule
spark.sql("____ ____").show()

Code bewerken en uitvoeren

Deze oefening maakt deel uit van de cursus

Introductie tot Spark SQL in Python

SkillTag.level.advancedSkillTag.label

4.7+

95 reviews

Begin de cursus gratis

In this chapter you will learn how to create and query a SQL table in Spark. Spark SQL brings the expressiveness of SQL to Spark. You will also learn how to use SQL window functions in Spark. Window functions perform a calculation across rows that are related to the current row. They greatly simplify achieving results that are difficult to express using only joins and traditional aggregations. We'll use window functions to perform running sums, running differences, and other operations that are challenging to perform in basic SQL.

Exercise 1: Een SQL-tabel maken en bevragen in Spark Exercise 2: Maak een SQL-tabel van een dataframe Exercise 3: Bepaal de kolomnamen van een tabel

Huidige oefening

Exercise 4: Windowfunctie-SQL Exercise 5: Voortschrijdende sommen met windowfunctie-SQL Exercise 6: Repareer de kapotte query Exercise 7: Puntnotatie en SQL Exercise 8: Aggregatie, stap voor stap Exercise 9: Dezelfde kolom twee keer aggregeren Exercise 10: Aggregatie met dot-SQL Exercise 11: Zet een windowfunctie om van dotnotatie naar SQL

In this chapter, you will be loading natural language text. Then you will apply a moving window analysis to find frequent word sequences.

Exercise 1: Loading natural language text Exercise 2: Loading a dataframe from a parquet file Exercise 3: Split and explode a text column Exercise 4: Using monotonically_increasing_id()Exercise 5: Moving window analysis Exercise 6: Creating context window feature data Exercise 7: Repartitioning the data Exercise 8: Common word sequences Exercise 9: What type of data is this Exercise 10: Finding common word sequences Exercise 11: Unique 5-tuples in sorted order Exercise 12: Most frequent 3-tuples per chapter

In the previous chapters you learned how to use the expressiveness of window function SQL. However, this expressiveness now makes it important that you understand how to properly cache dataframes and cache SQL tables. It is also important to know how to evaluate your application. You learn how to do do this using the Spark UI. You'll also learn a best practice for logging in Spark. Spark SQL brings with it another useful tool for tuning query performance issues, the query execution plan. You will learn how to use the execution plan for evaluating the provenance of a dataframe.

Exercise 1: Caching Exercise 2: Practice query plans 2 Exercise 3: Practicing caching: part 1 Exercise 4: Practicing caching: the SQL Exercise 5: Practicing caching: putting it all together Exercise 6: Caching and uncaching tables Exercise 7: The Spark UI Exercise 8: Spark UI storage tab Exercise 9: Inspecting cache in the Spark UI Exercise 10: Logging Exercise 11: Practice logging Exercise 12: Practice logging 2 Exercise 13: Query plans Exercise 14: Practice query plans Exercise 15: Practice reading query plans 2

Previous chapters provided you with the tools for loading raw text, tokenizing it, and extracting word sequences. This is already very useful for analysis, but it is also useful for machine learning. What you've learned now comes together by using logistic regression to classify text. By the conclusion of this chapter, you will have loaded raw natural language text data and used it to train a text classifier.

Exercise 1: Extract Transform Select Exercise 2: Practicing creating a UDF Exercise 3: Practicing array column Exercise 4: Creating feature data for classification Exercise 5: Creating a UDF for vector data Exercise 6: Applying a UDF to vector data Exercise 7: Transforming text to vector format Exercise 8: Text Classification Exercise 9: Label the data Exercise 10: Split the data Exercise 11: Train the classifier Exercise 12: Predicting and evaluating Exercise 13: Evaluate the classifier Exercise 14: Predict test data Exercise 15: Recap