Numeric and decimal precision in PostgreSQL - Step-by-Step Execution

Concept Flow - Numeric and decimal precision

Define numeric/decimal column with precision

↓

Insert value into column

↓

Check if value fits precision and scale

↓

Store value

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Retrieve value with precision

This flow shows how PostgreSQL handles numeric/decimal values with defined precision and scale during insert and retrieval.

Execution Sample

PostgreSQL

CREATE TABLE prices (
  price NUMERIC(5,2)
);

INSERT INTO prices VALUES (123.456);
SELECT price FROM prices;

Create a table with a numeric column of precision 5 and scale 2, insert a value with more decimals, then select it.

Execution Table

Step	Action	Input Value	Precision Check	Stored Value	Notes
1	Create table	N/A	N/A	Table with price NUMERIC(5,2)	Defines max 5 digits total, 2 after decimal
2	Insert value	123.456	123.456 fits? Max digits=5, scale=2	123.46	Value rounded to 2 decimal places
3	Select value	N/A	N/A	123.46	Retrieved value shows rounded number
4	Insert large value	12345.67	Digits=7 > 5	Error	Value too large for defined precision

💡 Execution stops after error on inserting value exceeding precision

Variable Tracker

Variable	Start	After Insert 1	After Insert 2	Final
price	NULL	123.46	Error (no change)	123.46

Key Moments - 2 Insights

Why does 123.456 become 123.46 when inserted?

Because the column is defined with scale 2, PostgreSQL rounds the value to 2 decimal places as shown in execution_table row 2.

What happens if the number has more digits than precision allows?

PostgreSQL raises an error and does not store the value, as shown in execution_table row 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the stored value after inserting 123.456?

A 123.456

B 123.46

C 123.45

D Error

💡 Hint

Check execution_table row 2 under Stored Value column

At which step does an error occur due to precision overflow?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

See execution_table row 4 Notes column

If the scale was changed to 3, how would the stored value for 123.456 change?

A It would store 123.456 exactly

B It would round to 123.46

C It would cause an error

D It would store 123.45

💡 Hint

Scale controls decimal places, see concept_flow and execution_table row 2

Concept Snapshot

NUMERIC(p,s) or DECIMAL(p,s) defines a number with p total digits and s digits after decimal.
Values inserted are rounded to scale s.
If value exceeds precision p, an error occurs.
Use for exact decimal storage like money.
Example: NUMERIC(5,2) stores up to 999.99.

Full Transcript

This visual execution trace shows how PostgreSQL handles numeric and decimal precision. First, a table is created with a numeric column defined as NUMERIC(5,2), meaning it can store numbers with up to 5 digits total and 2 digits after the decimal point. When inserting the value 123.456, PostgreSQL rounds it to 123.46 to fit the scale of 2 decimal places. Selecting the value returns 123.46. If a value like 12345.67 is inserted, which has 7 digits, it exceeds the precision and causes an error, so it is not stored. The variable tracker shows the price value changing from NULL to 123.46 after the first insert, and no change after the failed insert. Key moments clarify why rounding happens and what causes errors. The quiz questions test understanding of rounding, error steps, and scale effects. The snapshot summarizes the key rules for numeric precision and scale in PostgreSQL.