DA0-002 Data Acquisition and Preparation Practice Question
A data analyst is cleaning text data in a SQL database. Which THREE string functions are commonly used to standardize and clean text? (Choose three.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
REPLACE
REPLACE is correct because it substitutes specific substrings (e.g., removing stray characters or fixing inconsistent tokens) within a string, which is a core standardization step. UPPER is correct because it converts all characters to uppercase, enforcing consistent casing so values like 'usa' and 'USA' match during cleaning and comparison. TRIM is correct because it removes leading and trailing spaces (or specified characters), eliminating whitespace artifacts that break joins, grouping, and equality checks. LENGTH does not belong because it only returns the number of characters in a string and does not modify or standardize the data. CONCAT does not belong because it merely joins strings together, which is a transformation for combining values rather than cleaning or standardizing text.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
REPLACE
Why this is correct
REPLACE substitutes specified substrings within a string, letting analysts strip or correct unwanted characters during standardisation. This satisfies the text-cleaning requirement by enabling consistent transformation of messy values, and is a standard SQL string function.
- ✓
UPPER
Why this is correct
UPPER converts all characters in a string to uppercase, enforcing consistent casing across records. This satisfies the standardisation requirement by removing case variation that would otherwise cause mismatches during comparison, joining or deduplication of text data.
- ✗
LENGTH
Why it's wrong here
LENGTH returns the character count of a string, which only measures data; it neither alters nor standardises values. It is tempting because length checks help validate fields and detect truncated entries during profiling, but cleaning requires functions such as TRIM, UPPER or REPLACE that transform the stored text.
- ✓
TRIM
Why this is correct
TRIM removes leading and trailing whitespace, directly standardising text values so that padded entries match their unpadded equivalents during joins, grouping and deduplication. This satisfies the stem's requirement to standardise and clean text data in SQL.
- ✗
CONCAT
Why it's wrong here
CONCAT joins two or more strings into one value, which combines data rather than cleaning it. It is tempting because concatenation is common in SQL text work, such as building full names or composite keys, but standardising existing values needs TRIM, UPPER, LOWER or REPLACE instead.
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