在Netezza中如何将字符串型科学计数法转为可用数值？

Alright, let's figure out how to convert those string-stored scientific notation values into usable numbers in Netezza. I've dealt with this exact scenario before, so here are the most reliable approaches:

1. Direct Casting (Simplest for Standard Formats) #

Netezza’s built-in casting functions natively recognize standard scientific notation strings (like '1.23E+05' or '4.56e-3'). You can use either the CAST() function or the shorthand :: operator to convert these strings to numeric types like DOUBLE PRECISION, BIGINT, or INTEGER.

Example: Convert to DOUBLE PRECISION #

SELECT CAST(scientific_string_column AS DOUBLE PRECISION) AS converted_numeric
FROM your_table_name;

-- Shorthand version (equivalent, just cleaner syntax)
SELECT scientific_string_column::DOUBLE PRECISION AS converted_numeric
FROM your_table_name;

Example: Convert to Integer Types #

If your scientific notation values represent whole numbers, you can cast directly to BIGINT or INTEGER. For values with decimal parts, round first to avoid truncation issues:

-- Direct cast for whole-number values
SELECT CAST(scientific_string_column AS BIGINT) AS integer_value
FROM your_table_name;

-- Round first if you need to handle decimal values
SELECT ROUND(CAST(scientific_string_column AS DOUBLE PRECISION))::BIGINT AS rounded_integer
FROM your_table_name;

2. TO_NUMBER() for Non-Standard or Custom Formats #

If your strings have quirks (like extra spaces, or you want explicit control over parsing), use TO_NUMBER() with a format mask that accounts for scientific notation.

Example: #

SELECT TO_NUMBER(scientific_string_column, '9.999EEEE') AS converted_numeric
FROM your_table_name;

• The EEEE segment tells Netezza to parse the exponent part. Adjust the number of 9s before/after the decimal point to match your data's precision (e.g., 99.99EEEE for larger whole numbers).

Handling Invalid or Malformed Strings #

If your table has strings that aren't valid scientific notation, these casts will throw errors. Here's how to handle that:

Use TRY_CAST (Newer Netezza Versions) #

If you're running a recent Netezza release, TRY_CAST is your best bet—it returns NULL instead of crashing for invalid values:

SELECT TRY_CAST(scientific_string_column AS DOUBLE PRECISION) AS converted_numeric
FROM your_table_name;

For Older Versions (No TRY_CAST) #

Use a CASE statement with a regex to validate the string before casting:

SELECT 
  CASE 
    WHEN scientific_string_column ~ '^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)$'
    THEN CAST(scientific_string_column AS DOUBLE PRECISION)
    ELSE NULL -- Replace with a default value if needed
  END AS converted_numeric
FROM your_table_name;

The regex checks that the string follows standard scientific notation rules before attempting conversion.

内容的提问来源于stack exchange，提问作者kltft